db: adjust pebbledb metric

[yoomee1313]

Proposed changes

• This PR adds some level related pebbledb metrics. Also, it adds PebbleDB dbtype option since it was missing.
• Some metrics are not matched 100% between leveldb and pebbledb, so be pay attention when comparing those metrics.

Types of changes

Please put an x in the boxes related to your change.

• [ ] Bugfix
• [ ] New feature or enhancement
• [ ] Others

Checklist

Put an x in the boxes that apply. You can also fill these out after creating the PR. If you're unsure about any of them, don't hesitate to ask. We're here to help! This is simply a reminder of what we are going to look for before merging your code.

• [ ] I have read the CONTRIBUTING GUIDELINES doc
• [ ] I have read the CLA and signed by comment I have read the CLA Document and I hereby sign the CLA in first time contribute
• [ ] Lint and unit tests pass locally with my changes ($ make test)
• [ ] I have added tests that prove my fix is effective or that my feature works
• [ ] I have added necessary documentation (if appropriate)
• [ ] Any dependent changes have been merged and published in downstream modules

Related issues

• Please leave the issue numbers or links related to this PR here.

Further comments

For example, one of the level related pebbledb metric, klaytn_klay_db_chaindata_statetrie_0levelN_size (N=0~6) is now available in pebbleDB.

[blukat29]

@hyunsooda PTAL