Feature(2.3): metrics of delta_compactions; some improvements

[zipper-meng]

Required checklist

• Sample config files updated (config,meta/config and default config)
• If there are user-facing changes, the documentation needs to be updated prior to approving the PR( Link )
• If there are any breaking changes to public APIs, please add the api change label.
• Signed CLA (if not already signed)

Which issue does this PR close?

Related #.

Rationale for this change

Compaction

Add metrics for delta compactions, to enable set config storage.collect_compaction_metrics = true.

Job

Fix the concurrent compactions sometimes less than config storage.max_concurrent_compaction.

Schedule

• Do not trigger normal compaction after delta_compaction.
• If a vnode has fewer delta files to trigger delta_compaction, run normal compaction on the vnode.

Are there any user-facing changes?