chore: adjust storage engine related metrics

[waynexia]

I hereby agree to the terms of the GreptimeDB CLA

What's changed and what's your intention?

As title. This patch mainly focus on metrics in mito and metric engine

Checklist

• I have written the necessary rustdoc comments.
• I have added the necessary unit tests and integration tests.
• This PR does not require documentation updates.

Refer to a related PR or issue link (optional)

[codecov]

Codecov Report

Attention: 1 lines in your changes are missing coverage. Please review.

Comparison is base (e5a2b04) 85.78% compared to head (531b8d0) 85.34%.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #3261      +/-   ##
==========================================
- Coverage   85.78%   85.34%   -0.45%     
==========================================
  Files         856      856              
  Lines      140188   140205      +17     
==========================================
- Hits       120261   119655     -606     
- Misses      19927    20550     +623