chore: miscellaneous repository maintenance

[rnbguy]

• Closes RUSTSEC-2020-0168: mach is unmaintained #1172
• Fixes broken links on markdown files.
• Add missing changelog entry from imp(ics23): fallible conversion for ProofSpec, LeafOp, InnerSpec #1160
• Rename makefile to Makefile.
• Remove unnecessary nix use in cw-check.
• Remove rokroskar/workflow-run-cleanup-action from Rust workflow over native concurrency support.
• Setup merge_group with correct workflow status checks.
  • Disable merge_group trigger.
  • Always run important workflows on main.
  • Remove markdown link checks from main.
• Use .yml over .yaml .yaml over .yml as workflow file extensions.
• Use actions-rust-lang/setup-rust-toolchain.
• Update download artifact example for Tendermint wasm client.

Setting up merge_group is a bit complicated. To auto-remove a PR from merge_group, we need to add them as status_check for merges onto main. But if a job is not executed (because of filtering of paths or trigger events), it will never be added in merge_group - because we need all status checks to be passed before merge.

The merge_group only works for a workflow something as following:

name: Status Check Jobs
on:
  pull_request:
  merge_group:
    types: [checks_requested]


jobs:
  my-job:
    if: ${{ github.event_name != 'pull_request' }}
    steps:
      run: echo "Hello World"

So the workflow is marked as successfully executed on PR, albeit it didn't run any job. When, the PR is put in merge_group, it will actually run my-job.

---

PR author checklist:

• Added changelog entry, using unclog.
• Added tests.
• Linked to GitHub issue.
• Updated code comments and documentation (e.g., docs/).
• Tagged one reviewer who will be the one responsible for shepherding this PR.

Reviewer checklist:

• Reviewed Files changed in the GitHub PR explorer.
• Manually tested (in case integration/unit/mock tests are absent).

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 64.33%. Comparing base (ddd3f48) to head (3bf544b).

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #1174   +/-   ##
=======================================
  Coverage   64.33%   64.33%           
=======================================
  Files         229      229           
  Lines       22083    22083           
=======================================
  Hits        14208    14208           
  Misses       7875     7875           

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[seanchen1991]

Looks good to me. Thanks for making all these improvements! 🎉