support exposing Pebble stats too, beside Leveldb

[ucwong]

No description provided.

[codecov]

Codecov Report

Merging #1747 (f6b2946) into master (44d33c2) will increase coverage by 0.02%.
Report is 7 commits behind head on master.
The diff coverage is 0.00%.

❗ Current head f6b2946 differs from pull request most recent head 94d1f5b. Consider uploading reports for the commit 94d1f5b to get more accurate results

@@            Coverage Diff             @@
##           master    #1747      +/-   ##
==========================================
+ Coverage   52.68%   52.70%   +0.02%     
==========================================
  Files         486      486              
  Lines       60460    60464       +4     
==========================================
+ Hits        31852    31868      +16     
+ Misses      26169    26145      -24     
- Partials     2439     2451      +12     

Files	Coverage Δ
ctxcdb/pebble/pebble.go	38.46% <0.00%> (ø)
core/types/transaction.go	64.24% <0.00%> (ø)
ctxcdb/leveldb/leveldb.go	22.92% <0.00%> (-0.46%)	⬇️
ctxc/fetcher/tx_fetcher.go	0.00% <0.00%> (ø)

... and 12 files with indirect coverage changes