all: Use context from session in sqlx functions

[tamirms]

PR Checklist

PR Structure

• This PR has reasonably narrow scope (if not, break it down into smaller PRs).
• This PR avoids mixing refactoring changes with feature changes (split into two PRs
  otherwise).
• This PR's title starts with name of package that is most changed in the PR, ex.
  services/friendbot, or all or doc if the changes are broad or impact many
  packages.

Thoroughness

• This PR adds tests for the most critical parts of the new functionality or fixes.
• I've updated any docs (developer docs, .md
  files, etc... affected by this change). Take a look in the docs folder for a given service,
  like this one.

Release planning

• I've updated the relevant CHANGELOG (here for Horizon) if
  needed with deprecations, added features, breaking changes, and DB schema changes.
• I've decided if this PR requires a new major/minor version according to
  semver, or if it's mainly a patch change. The PR is targeted at the next
  release branch if it's not a patch change.

What

Close #1950 , #1974

Use the context in db.Session when executing sql queries and statements on the session connection. A consequence of this change is that the session context is no longer optional.

Why

It should be possible to pass context.Context to set timeout for queries sent to a database. This is to prevent long running queries to occupy DB connection for a long period of time.

Known limitations

[TODO or N/A]

[bartekn]

LGTM! FYT, registered context.DeadlineExceeded to return 504 responses in ece2b85. Adding @accordeiro to reviewers because it touches his app. Alex, when you're back please check it out.

[accordeiro]

The ticker part looks good to me :)