docs: Update link to the new CNCF Slack channel

[terrytangyuan]

Signed-off-by: terrytangyuan terrytangyuan@gmail.com

Checklist:

• Either (a) I've created an enhancement proposal and discussed it with the community, (b) this is a bug fix, or (c) this is a chore.
• The title of the PR is (a) conventional, (b) states what changed, and (c) suffixes the related issues number. E.g. "fix(controller): Updates such and such. Fixes #1234".
• I've signed my commits with DCO
• I have written unit and/or e2e tests for my change. PRs without these are unlikely to be merged.
• My builds are green. Try syncing with master if they are not.
• My organization is added to USERS.md.

[sonarqubecloud]

Kudos, SonarCloud Quality Gate passed!

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[codecov]

Codecov Report

Merging #1090 (4fb66a6) into master (3a2936e) will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master    #1090   +/-   ##
=======================================
  Coverage   81.24%   81.24%           
=======================================
  Files         103      103           
  Lines        9192     9192           
=======================================
  Hits         7468     7468           
  Misses       1229     1229           
  Partials      495      495           

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[terrytangyuan]

I discussed this with @alexmt and he's going to reuse the existing link with instructions to join the CNCF workspace and channels. See argoproj/argo-cd#6044 (comment) for more context. Closing this for now.