Bump v6.0.0 (#941)

Bump version: 6.0.0.rc5 (#939)

docs: Add new Ruby and Redis versions requirement to upgrade guide (#937

)

Merge branch 'main' into release/v6.0.0

Records main as merged without taking any of its content. The tree is
unchanged.

main carries the v5.8.3 hotfix 25288bb, which gave the Redis metrics key a
TTL equal to the window size in the monolithic data store that 6.0.0 removes.
The decomposed window metrics store evicts buckets older than the window on
every write, so memory is bounded by the window rather than by request volume.
The hotfix is superseded, and a normal merge would only have resurrected the
files 6.0.0 deleted.

Bump version: 6.0.0.rc2

Bump version: 6.0.0.rc1

Version 5.8.3

Version 5.8.2

Version 5.8.0

Version 5.7.0