Observe the cluster at runtime, support namespace globs & partial resource specs

[nolar]

The runtime cluster observation lets the operator to know which resources & namespaces actually exist, which, in turn, lets the operator developers to specify the resources by their shorter names instead of their full API endpoints (group-version-plural):

import kopf

@kopf.on.event('pods')
@kopf.on.event('kex')  # short-names
@kopf.on.event('KopfExample')  # kind
def fn(**_): ...

Or even serve the resources by categories:

import kopf

@kopf.on.event(category='all')
def fn(**_): ...

Or even serve all the resources. It might be a terrible idea to try this on a real cluster unless some filtering is used:

import kopf

@kopf.on.event(kopf.EVERYTHING, labels={'only-this': kopf.PRESENT})
def fn(**_): ...

Some other forms of the specifiers are shown in the docs. In particular, kind, singular, plural, short names are supported, with or without groups and versions.

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Similarly, due to observation of the existing namespaces, multiple namespaces can be served, specified by globs and negations:

kopf run ...  -n myapp-*,!*-pr-*  -n  otherapp*

More pattern notations are also mentioned in the docs.

---

This PR is huge. It could not be made smaller. All unrelated and partially related things are already extracted into separate preparational PRs #576 #575 #572 #597 #598 #596 #608 #609 #610 #622 #623 #624 #626 #627. This PR has also triggered the final removal of the deprecated registries #611 #625 and other deprecated features #511 as a preparation to make it possible to implement it (refactor the reactor's core).

Consider this PR as a full remake of the framework's core the way as it should have been done originally, but it was too early to overengineer it that way.

Addresses the initial framework vision: #57, #85.

[lgtm-com]

This pull request introduces 5 alerts and fixes 1 when merging cbfbb08 into 9fe89e9 - view on LGTM.com

new alerts:

• 5 for Unused import

fixed alerts:

• 1 for Unused import

[lgtm-com]

This pull request introduces 4 alerts and fixes 1 when merging 199d9d7 into 214310c - view on LGTM.com

new alerts:

• 4 for Unused import

fixed alerts:

• 1 for Unused import

[lgtm-com]

This pull request introduces 2 alerts and fixes 1 when merging 7bcc7b7 into f5a6dcd - view on LGTM.com

new alerts:

• 2 for Unused import

fixed alerts:

• 1 for Unused import

[lgtm-com]

This pull request introduces 2 alerts when merging 3be426f into 53aef59 - view on LGTM.com

new alerts:

• 2 for Unused import

[lgtm-com]

This pull request introduces 2 alerts when merging 732d0b9 into 53aef59 - view on LGTM.com

new alerts:

• 2 for Unused import