Expose optional label matcher for label values handler

[periklis]

What this PR does / why we need it:
This is a follow-up to expose the optional matchers on the labels values API to the HTTP handler introduced by #4933

Which issue(s) this PR fixes:
Fixes #

Special notes for your reviewer:
Currently this works on the querier http API directly. However I still fail to pass the query from the frontend tripperware down the stack when request encoding happens. @jeschkies any advise welcome.

In addition I err to rename the parameter from query to match. However I hesitated to do so as per the LokiLabelNamesRequest implementing the queryrangebase/Request interface that in turns includes a Query() method.

Checklist

• Reviewed the CONTRIBUTING.md guide (required)
• Documentation added
• Tests updated
• CHANGELOG.md updated
• Changes that require user attention or interaction to upgrade are documented in docs/sources/upgrading/_index.md

[grafanabot]

Hello @periklis!
Backport pull requests need to be either:

• Pull requests which address bugs,
• Urgent fixes which need product approval, in order to get merged,
• Docs changes.

Please, if the current pull request addresses a bug fix, label it with the type/bug label.
If it already has the product approval, please add the product-approved label. For docs changes, please add the type/docs label.
If none of the above applies, please consider removing the backport label and target the next major/minor release.
Thanks!

[grafanabot]

Hello @periklis!
Backport pull requests need to be either:

• Pull requests which address bugs,
• Urgent fixes which need product approval, in order to get merged,
• Docs changes.

Please, if the current pull request addresses a bug fix, label it with the type/bug label.
If it already has the product approval, please add the product-approved label. For docs changes, please add the type/docs label.
If none of the above applies, please consider removing the backport label and target the next major/minor release.
Thanks!

[periklis]

@jeschkies @DylanGuedes Considering on how long we have #4933 in our code base remaining unexposed it may still be buggy returning duplicate label values when using a regex label matcher.

Assuming you use the k8s pod names as labels which are per se always unique, I want to filter the values for a set of namespaces I pass to labels values API via a regex matcher, e.g. 4 namespaces each 5 pods:

/loki/api/v1/label/kubernetes_pod_name/values?query={kubernetes_namespace_name=~"ns-a|ns-b|ns-c|ns-d"}

The resulting list includes duplicates (in total 25 pod names, of which 5 are duplicates):

[
  "logger-57f5c5f65d-2wvh6",
  "logger-57f5c5f65d-4tm75",
  **"logger-57f5c5f65d-64pnf",**
  ** "logger-57f5c5f65d-64pnf",**
  "logger-57f5c5f65d-6kr2n",
  "logger-57f5c5f65d-7mpdb",
  "logger-57f5c5f65d-8lqng",
  "logger-57f5c5f65d-9njgp",
  "logger-57f5c5f65d-c5xv7",
  **"logger-57f5c5f65d-cbzpg",**
  **"logger-57f5c5f65d-cbzpg",**
  "logger-57f5c5f65d-dmw8k",
  "logger-57f5c5f65d-g658h",
  "logger-57f5c5f65d-kcvpm",
  "logger-57f5c5f65d-mfbmf",
  **"logger-57f5c5f65d-p2n5x",**
  **"logger-57f5c5f65d-p2n5x",**
  "logger-57f5c5f65d-q7h6d",
  **"logger-57f5c5f65d-r72wk",**
  **"logger-57f5c5f65d-r72wk",**
  "logger-57f5c5f65d-t8nlk",
  "logger-57f5c5f65d-t9tl9",
  **"logger-57f5c5f65d-ttkkh",**
  **"logger-57f5c5f65d-ttkkh",**
  "logger-57f5c5f65d-wj6lj"
]

I have tried to debug this adding some matchers tests in f8ee569 for the series_index_store. However it looks the stores work fine for every schema and config so far. Any clue what could cause such a behavior? (maybe missing dedup work on the query frontend?)

[aminesnow]

What's up with commented lines? Is this WIP?

[JStickler]

[docs team] So, looking at both this PR and #4933, and there's just a single line of new documentation? I feel like this needs more doc.

[jeschkies]

I've got a few tiny open questions. Otherwise it looks good.

As for your error. Do you get duplicates without passing label marchers?

[DylanGuedes]

lgtm, just a few nits

[grafanabot]

The backport to release-2.7.x failed:

The process '/usr/bin/git' failed with exit code 1

To backport manually, run these commands in your terminal:

# Fetch latest updates from GitHub
git fetch
# Create a new branch
git switch --create backport-8824-to-release-2.7.x origin/release-2.7.x
# Cherry-pick the merged commit of this pull request and resolve the conflicts
git cherry-pick -x 1bcf683513b5e11fb1dcc5625761b9760cfbd958
# Push it to GitHub
git push --set-upstream origin backport-8824-to-release-2.7.x
git switch main
# Remove the local backport branch
git branch -D backport-8824-to-release-2.7.x

Then, create a pull request where the base branch is release-2.7.x and the compare/head branch is backport-8824-to-release-2.7.x.

[grafanabot]

The backport to release-2.8.x failed:

The process '/usr/bin/git' failed with exit code 1

To backport manually, run these commands in your terminal:

# Fetch latest updates from GitHub
git fetch
# Create a new branch
git switch --create backport-8824-to-release-2.8.x origin/release-2.8.x
# Cherry-pick the merged commit of this pull request and resolve the conflicts
git cherry-pick -x 1bcf683513b5e11fb1dcc5625761b9760cfbd958
# Push it to GitHub
git push --set-upstream origin backport-8824-to-release-2.8.x
git switch main
# Remove the local backport branch
git branch -D backport-8824-to-release-2.8.x

Then, create a pull request where the base branch is release-2.8.x and the compare/head branch is backport-8824-to-release-2.8.x.