Optimize Application Server worker pools

[adriansmares]

Summary

Closes #4606

Changes

• Add pkg/workerpool, which contains the generic worker pool that spawns workers on demand
• Refactor the application packages frontend to use the pkg/workerpool pool instead of the manually spawned tasks
  • A small deviation that you will see here is that there is a worker pool added between the io.Subscription and the actual worker pools of each package. This is intentional and allows us to decide to which package we need to send a particular uplink to in parallel.
• Refactor the webhooks frontend to use the pkg/workerpool pool instead of the manually spawned goroutines

Testing

Unit testing and local testing.

Regressions

This changes the piping used by the Application Server worker pools. The unit tests cover this.

Checklist

• Scope: The referenced issue is addressed, there are no unrelated changes.
• Compatibility: The changes are backwards compatible with existing API, storage, configuration and CLI, according to the compatibility commitments in README.md for the chosen target branch.
• Documentation: Relevant documentation is added or updated.
• Changelog: Significant features, behavior changes, deprecations and fixes are added to CHANGELOG.md.
• Commits: Commit messages follow guidelines in CONTRIBUTING.md, there are no fixup commits left.

[KrishnaIyer]

Fantastic. Looks good to me.