docs: Proposal Process Update - Specify post-acceptance non-material update procedure

[poulok]

Description:
Updates the proposal process to specify how non-material changes can be made to accepted proposals.

[codacy-production]

Coverage summary from Codacy

See diff coverage on Codacy

Coverage variation	Diff coverage
✅ +0.02% (target: -1.00%)	✅ ∅

Coverage variation details

	Coverable lines	Covered lines	Coverage
Common ancestor commit (7a4616b)	108968	67303	61.76%
Head commit (1a7eb0d)	109068 (+100)	67383 (+80)	61.78% (+0.02%)

Coverage variation is the difference between the coverage for the head and common ancestor commits of the pull request branch: <coverage of head commit> - <coverage of common ancestor commit>

Diff coverage details

	Coverable lines	Covered lines	Diff coverage
Pull request (#15447)	0	0	∅ (not applicable)

Diff coverage is the percentage of lines that are covered by tests out of the coverable lines that the pull request added or modified: <covered lines added or modified>/<coverable lines added or modified> * 100%

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_{Codacy stopped sending the deprecated coverage status on June 5th, 2024. Learn more}

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 58.25%. Comparing base (7a4616b) to head (1a7eb0d).
Report is 10 commits behind head on develop.

Additional details and impacted files

@@              Coverage Diff              @@
##             develop   #15447      +/-   ##
=============================================
+ Coverage      58.22%   58.25%   +0.02%     
- Complexity     21573    21610      +37     
=============================================
  Files           2779     2781       +2     
  Lines         109151   109269     +118     
  Branches       11163    11176      +13     
=============================================
+ Hits           63554    63650      +96     
- Misses         41738    41761      +23     
+ Partials        3859     3858       -1     

see 37 files with indirect coverage changes