Add metrics for bucketassign.minibatch.cache.hit.count / cache.miss.count (cache hit ratio)

[danny0405]

Feature Description

What the feature achieves:

Why this feature is needed:

User Experience

How users will use this feature:

• Configuration changes needed
• API changes
• Usage examples

Hudi RFC Requirements

RFC PR link: (if applicable)

Why RFC is/isn't needed:

• Does this change public interfaces/APIs? (Yes/No)
• Does this change storage format? (Yes/No)
• Justification: