chore: using bitly to manage expiring Slack invitation links

[rusackas]

SUMMARY

The Slack invitation links posted all over the codebase, issues/PRs, and throughout the known universe, are always expiring. They either expire due to TTL, or as soon as 400 people join.

This PR replaces the links in the codebase with a bitly link.

That bitly link can be updated through a bitly account, which the PMC (and committers?) should have access to. This will be added to the new 1Password account - any PMC members who need access to this, please reach out.

When (not if) the link expires, please update the bitly link accordingly, and all the aliases floating around out there should remain functional. This will be a lot less disruptive and hopefully lead to more people joining!

BEFORE/AFTER SCREENSHOTS OR ANIMATED GIF

TESTING INSTRUCTIONS

Try this! bit.ly/join-superset-slack

ADDITIONAL INFORMATION

• Has associated issue: Fixes Links to slack are dead #22672
• Required feature flags:
• Changes UI
• Includes DB Migration (follow approval process in SIP-59)
  • Migration is atomic, supports rollback & is backwards-compatible
  • Confirm DB migration upgrade and downgrade tested
  • Runtime estimates and downtime expectations provided
• Introduces new feature or API
• Removes existing feature or API

[codecov]

Codecov Report

Merging #22631 (6aff4b0) into master (804e89d) will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master   #22631   +/-   ##
=======================================
  Coverage   67.03%   67.03%           
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  Files        1859     1859           
  Lines       71043    71043           
  Branches     7776     7776           
=======================================
  Hits        47622    47622           
  Misses      21397    21397           
  Partials     2024     2024           

Flag	Coverage Δ
hive	52.48% <ø> (ø)
javascript	53.85% <ø> (ø)
mysql	78.04% <ø> (ø)
postgres	78.11% <ø> (ø)
presto	52.37% <ø> (ø)
python	81.37% <ø> (ø)
sqlite	76.49% <ø> (ø)
unit	51.48% <ø> (ø)

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