feat: support show columns and show index in sharding mode

[dk-lockdown]

ref: #191
ref: #192

Ⅰ. Describe what this PR did

Support show columns and show index

II. Describe how to verify it

Check integration test result

[codecov-commenter]

Codecov Report

Merging #269 (554b0a9) into dev (f896fc3) will decrease coverage by 0.08%.
The diff coverage is 0.00%.

@@            Coverage Diff             @@
##              dev     #269      +/-   ##
==========================================
- Coverage   43.03%   42.95%   -0.09%     
==========================================
  Files          84       85       +1     
  Lines       10059    10078      +19     
==========================================
  Hits         4329     4329              
- Misses       5276     5295      +19     
  Partials      454      454              

Impacted Files	Coverage Δ
pkg/optimize/optimize_show_table_meta.go	0.00% <0.00%> (ø)
pkg/optimize/optimize_show_table_status.go	0.00% <0.00%> (ø)
pkg/optimize/optimizer.go	30.76% <0.00%> (-2.57%)	⬇️
pkg/plan/show_table_meta.go	0.00% <0.00%> (ø)

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[bohehe]

LGTM