chore: add new PR workflow

[david-luna]

Which problem is this PR solving?

Changes the PR workflow to a single file to improve it making it faster with less resource consumption. The goal is to provide feedback to the PR author by compiling, testing and reporting coverage only for the affected packages in the PR (as for now it does a compilation, test, and coverage report for all in nodejs v18). More details on the plan can be found in #2870

Closes: #2870

Short description of the changes

• add new PR workflow with:
  • single compile step for affected packages. results are cached
  • unit and TAV test for affected packages for a matrix of nodejs versions. Reusing compilation results from cache. coverage reports are cached
  • get coverage reports from all nodejs versions (in cache) and merge them. then upload them to codecov
• add scripts to support such workflow
  • *:ci:affected script at root to execute tasks only for affected packages (leveraging nx CLI)
• update codecov.yml to assign flags to each package so reports can be updated independently

Checklist

Codecov flags feature require a first manual upload to create them so it would be helpful to resume #2214 to at least have a script at the root to testa and upload all reports. There is also some PRs that affect the flag configuration so it would be preferable to have them merged 1st

• merge chore: Add docker compose and test services scripts #2886 or at least have a test:with-services script at the root
• merge redis refactor feat(redis): consolidate redis v2,3 and redis v4 instrumentation to one package #2878
• if possible merge chore: rename workspace dirs to match the base of the package name #2223

[github-actions]

This package does not have an assigned component owner and is considered unmaintained. As such this package is in feature-freeze and this PR will be closed with 14 days unless a new owner or a sponsor (a member of @open-telemetry/javascript-approvers) for the feature is found. It is the responsibility of the author to find a sponsor for this feature.
Are you familiar with this package? Consider becoming a component owner.

[pichlermarc]

if easy to do we could also use these for completeness, but just using 18 and 20 is likely more than okay 🙂

[pichlermarc]

keeping the name unit-test would help with repo settings, since unit-test (18) and unit-test (18.19.0) required checks. Repo managment is now automated from another repo, so changing the check's name would require us to open a PR in that other repo before merging this (which would then block other PRs from getting merged)

If we want to change the name we can do so in a smaller follow-up PR. :)