Add prefix ! and + to GitHub labels

[t2gran]

Summary

To make it easier to add labels I have divided the labels into 3 categoris:

• ! Type of issue or PR - exact one of these SHOULD be assigned to all PRs and Issues
• + Classify a PR or Issue into categories we frequently use. Labels used in the CI/CD fall into this category, as well as the tagging components for easier review (+Roadmap, +Sandbox, +Debug UI, +Real-Time, +Skip Changelog, +Bump Serialization Id ...). PRs and Issues might have zero, one or more of these assigned.
• Everything else.

Issue

Related to #6866

Unit tests

🟥 Not relevant

Documentation

Partly documented in #6866

Changelog

🟥 Not relevant

Bumping the serialization version id

🟥 Not relevant

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 72.10%. Comparing base (5eb8e59) to head (09bf59c).
⚠️ Report is 3 commits behind head on dev-2.x.

Additional details and impacted files

@@            Coverage Diff             @@
##             dev-2.x    #6891   +/-   ##
==========================================
  Coverage      72.10%   72.10%           
- Complexity     19536    19538    +2     
==========================================
  Files           2106     2106           
  Lines          79004    79004           
  Branches        8009     8009           
==========================================
+ Hits           56964    56966    +2     
  Misses         19218    19218           
+ Partials        2822     2820    -2     

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[leonardehrenfried]

I think we ought to merge this sooner rather than later, because CI depends on these names.