[extension] Move optional interfaces to extensioncapabilities

[mx-psi]

Description

Moves extension optional interfaces to a new module, extensioncapabilities.

The intent is to be able to evolve these interfaces independently from the core interfaces on core.

These are used by at most one component/project, so I think they are not mature yet for 1.0

[codecov]

Codecov Report

Attention: Patch coverage is 50.00000% with 2 lines in your changes missing coverage. Please review.

Project coverage is 92.23%. Comparing base (a26068b) to head (70595c2).
Report is 1 commits behind head on main.

Files with missing lines	Patch %	Lines
service/extensions/extensions.go	33.33%	0 Missing and 2 partials ⚠️

Additional details and impacted files

@@           Coverage Diff           @@
##             main   #11000   +/-   ##
=======================================
  Coverage   92.23%   92.23%           
=======================================
  Files         406      406           
  Lines       19101    19101           
=======================================
  Hits        17618    17618           
  Misses       1123     1123           
  Partials      360      360           

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[TylerHelmuth]

Would love a shorter name if we can think of one. I can't, but maybe someone else can

[mx-psi]

Other than just "capabilities" I am out of ideas

[axw]

Could be shortened to "extensioncaps" a la the Linux capabilities family of commands, e.g. https://man7.org/linux/man-pages/man8/getpcaps.8.html. Seems OK as it is though.

[mx-psi]

Yeah, I feel like this is okay, we can rename later if we want to since this is not going 1.0 now. It's definitely on the longer side for a package name but it's not the longest if you take contrib component names into account