feat(channel)!: New pinned messages routes

[Jiralite]

Please describe the changes this PR makes and why it should be merged:

• Document new pin endpoints discord/discord-api-docs#7585
• feat: Support new pinned messages routes discord-api-types#1254

Status and versioning classification:

• Code changes have been tested against the Discord API, or there are no code changes
• I know how to update typings and have done so, or typings don't need updating
• This PR includes breaking changes (methods removed or renamed, parameters moved or removed)

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[codecov]

Codecov Report

Attention: Patch coverage is 0% with 12 lines in your changes missing coverage. Please review.

Project coverage is 44.42%. Comparing base (de2b2dd) to head (21a53db).
Report is 3 commits behind head on main.

Files with missing lines	Patch %	Lines
packages/core/src/api/channel.ts	0.00%	12 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #10988      +/-   ##
==========================================
- Coverage   44.42%   44.42%   -0.01%     
==========================================
  Files         308      308              
  Lines       17581    17583       +2     
  Branches     1748     1748              
==========================================
  Hits         7811     7811              
- Misses       9757     9759       +2     
  Partials       13       13              

Flag	Coverage Δ
core	0.88% <0.00%> (-0.01%)	⬇️

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Resolved.