chore: add Prettier action, update/cleanup workflows, format files

[ThirdEyeSqueegee]

Issue #, if available:
N/A

Description of changes:

• Add Prettier action for .md and .yml files
• Add Prettier instructions to CONTRIBUTING.md
• Bump workflow versions
• Add pull_request trigger for rust.yml
• Remove push trigger for rust.yml
• Format files
• Add rutajdash/prettier-cli-action to actions allowlist

By submitting this pull request, I confirm that my contribution is made under the terms of the Apache 2.0 license.

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 72.00000% with 21 lines in your changes missing coverage. Please review.

Project coverage is 41.82%. Comparing base (bc50c3e) to head (f653066).

Files with missing lines	Patch %	Lines
aws_secretsmanager_agent/src/config.rs	20.00%	8 Missing ⚠️
aws_secretsmanager_agent/src/server.rs	0.00%	8 Missing ⚠️
aws_secretsmanager_caching/src/output.rs	0.00%	4 Missing ⚠️
aws_secretsmanager_caching/src/lib.rs	97.87%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main      #95      +/-   ##
==========================================
- Coverage   42.19%   41.82%   -0.38%     
==========================================
  Files          14       14              
  Lines        8986     8570     -416     
==========================================
- Hits         3792     3584     -208     
+ Misses       5194     4986     -208     

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[simonmarty]

This needs IDE-independent instructions to run the formatter.