refactor!: remove async cache writeback on chunk fetcher

[slim-bean]

What this PR does / why we need it:

PR #5083 introduced async writeback for chunks from the fetcher, however, I think at the time it was overlooked that the cache implementations (memcached and redis are wrapped with a Background cache wrapper which already does async writeback of cache objects.

This PR removes the implementation from #5083 in favor of the Background wrapper which supports additional configurations such as setting a count or size limit of background writes

NOTES: THIS IS A BREAKING CHANGE AS IT DOES REMOVE EXISTING CONFIGS

Which issue(s) this PR fixes:
Fixes #

Special notes for your reviewer:

Checklist

• Reviewed the CONTRIBUTING.md guide (required)
• Documentation added
• Tests updated
• CHANGELOG.md updated
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• Changes that require user attention or interaction to upgrade are documented in docs/sources/setup/upgrade/_index.md
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