Support for IDisk in Keeper

[antonio2368]

Changelog category (leave one):

• Improvement

Changelog entry (a user-readable short description of the changes that goes to CHANGELOG.md):

Add support for external disks in Keeper for storing snapshots and logs.

Continuation of #45884

• possibility to define different disks for current and old logs
• restrict current disk to local disk
• try supporting snapshots with s3_plain (uses moveFile which is not supported by s3_plain disks)

Disks heavily depend on the Context which pulls huge amount of dependencies with it. To keep those dependencies at minimum, standalone Keeper will use a stripped-down Context with all the functions necessary for Disks.

Also, I explicitly added only Local disk and S3 disks (without cache) as a starting point. In future PRs we can try extending the support but I didn't see a reason to support all of the disks immediately because the benefits are questionable while I would need to add even more dependencies.

Docs: ClickHouse/clickhouse-docs#1206

cc @alesapin @kssenii (sanity check for the Disks part) @LiuYangkuan

Documentation entry for user-facing changes

• Documentation is written (mandatory for new features)

Information about CI checks: https://clickhouse.com/docs/en/development/continuous-integration/

[robot-ch-test-poll3]

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[antonio2368]

This PR added some optimizations for reading snapshot from file which obviously don't work for DiskS3 so I added back the old behaviour (keeping latest snapshot in memory) for disks that are not DiskLocal.

[pufit]

Looks good!