chore: Revert Celery 5 upgrade

[robdiciuccio]

SUMMARY

Reverts Celery 5.x upgrade in #15927 due to breaking changes per SIP-57.

Per the Celery 5.0 upgrade docs:

Celery 5.0 introduces a new CLI implementation which isn’t completely backwards compatible.

ADDITIONAL INFORMATION

• Has associated issue:
• 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 #16039 (28e2609) into master (4cb79e5) will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master   #16039   +/-   ##
=======================================
  Coverage   76.90%   76.90%           
=======================================
  Files         995      995           
  Lines       52842    52842           
  Branches     6709     6709           
=======================================
  Hits        40640    40640           
  Misses      11976    11976           
  Partials      226      226           

Flag	Coverage Δ
hive	81.32% <ø> (ø)
mysql	81.62% <ø> (ø)
postgres	81.64% <ø> (ø)
presto	81.48% <ø> (ø)
python	82.16% <ø> (ø)
sqlite	81.28% <ø> (ø)

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