Prepare 1.21.0-RC1

[cortinico]

Time to prepare a new release. This time it was harder than expected :(

• d4fcd48 Had to make sure the Gradle Plugin has a valid POM, as we now publish it to Central as well. Without a valid pom the whole publishing can't be performed.
• 87f32e1 Revert enabling MissingPackageDeclaration by default - See Active rules by default #4875
• e79afd7 Fix InvalidPackageDeclaration on functionalTests - This is really concerning as it means that our functionalTest for the Gradle Plugin are still consuming a version from Maven Central are not effectively testing the latest changes on main (cc @3flex for visiblity).

[codecov]

Codecov Report

Merging #4900 (a4d2d9f) into main (1258c2f) will not change coverage.
The diff coverage is n/a.

@@            Coverage Diff            @@
##               main    #4900   +/-   ##
=========================================
  Coverage     84.82%   84.82%           
  Complexity     3494     3494           
=========================================
  Files           496      496           
  Lines         11515    11515           
  Branches       2130     2130           
=========================================
  Hits           9768     9768           
  Misses          686      686           
  Partials       1061     1061           

Impacted Files	Coverage Δ
...sch/detekt/rules/bugs/MissingPackageDeclaration.kt	92.85% <ø> (ø)

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[cortinico]

Can we merge this as I can't create a Tag/Github release otherwise?

[BraisGabin]

Sure!