[repo] Release automation improvements

[CodeBlanch]

Changes

• Sets up the release automation to use OpenTelemetryBot
• Refactors post-release stable version PR update job from package workflow into a new workflow triggered by the release publish

Details

See: open-telemetry/community#2127 (comment)

By default actions performed in workflows (push, create PR, create release, etc.) don't trigger other workflows. This means when the automation does things like open PRs builds won't be run. Pushing a tag can't trigger the release job. There were some tricks employed previously like calling other workflows but it didn't work across the board. What this PR does is switch to OpenTelemetryBot which is more or less a normal account. Using OpenTelemetryBot allows the same triggers to work for the manual process and the automation.

Test runs:

• [repo] Prepare release core-1.9.0-beta.1 CodeBlanchOrg/opentelemetry-dotnet#16
• [repo] Prepare release core-1.9.0 CodeBlanchOrg/opentelemetry-dotnet#19 -> [repo] Core stable release 1.9.0 updates CodeBlanchOrg/opentelemetry-dotnet#20

Merge requirement checklist

• CONTRIBUTING guidelines followed (license requirements, nullable enabled, static analysis, etc.)

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 85.74%. Comparing base (6250307) to head (1f26be8).
Report is 244 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #5657      +/-   ##
==========================================
+ Coverage   83.38%   85.74%   +2.35%     
==========================================
  Files         297      254      -43     
  Lines       12531    11054    -1477     
==========================================
- Hits        10449     9478     -971     
+ Misses       2082     1576     -506     

Flag	Coverage Δ
unittests	?
unittests-Project-Experimental	85.66% <ø> (?)
unittests-Project-Stable	85.36% <ø> (?)
unittests-Solution	85.74% <ø> (?)
unittests-UnstableCoreLibraries-Experimental	20.13% <ø> (?)

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see 116 files with indirect coverage changes