[2pt] VShard: deprecate config option 'collect_bucket_garbage_interval'

[TarantoolBot]

VShard: deprecate config option 'collect_bucket_garbage_interval'

Product: Tarantool, vshard (external module)
Since: 0.1.17 (vshard version; vshard is compatible with Tarantool versions >= 1.9)
Audience/target: developers; Tarantool implementation teams
Root document: https://www.tarantool.io/en/doc/latest/reference/reference_rock/vshard/vshard_ref/#cfg-basic-collect-bucket-garbage-interval
SME: @Gerold103
Peer reviewer: @

Details

It was used to specify the interval between bucket garbage
collection steps. It was needed because garbage collection in
vshard was proactive. It didn't react to newly appeared garbage
buckets immediately.

Since now (0.1.17) garbage collection became reactive. It starts
working with garbage buckets immediately as they appear. And
sleeps rest of the time. The option is not used now and does not
affect behaviour of anything.

I suppose it can be deleted from the documentation. Or left with
a big label 'deprecated' + the explanation above.

An attempt to use the option does not cause an error, but logs a
warning.

• Related development issues and/or commits:
  tarantool/vshard@2132aa9

Definition of done

• Mark the collect_bucket_garbage_interval of vshard as depricated with the explanation from Details above. Make sense to also mention the vshard version.
• Describe also log warning