Feat(pisa-proxy, sharding): add database_table sharding rewrite

[xuanyuan300]

What is changed and how it works?

What's Changed:

1. Add sharding rewrite for database_table sharding strategy.

This PR fix some issue also.

1. Fix return incorrect result when execute sql that include count function. Close Count function merge failed #378
2. Fix rewrite sql incorrect when execute insert statements in database sharding strategy.
3. Fix return incorrect result when execute sql that include avg,min,max aggregation function.

[codecov]

Codecov Report

Merging #380 (4ec5dd3) into master (df61eb4) will increase coverage by 7.70%.
The diff coverage is 84.76%.

@@            Coverage Diff             @@
##           master     #380      +/-   ##
==========================================
+ Coverage   66.97%   74.68%   +7.70%     
==========================================
  Files           7        6       -1     
  Lines         427      719     +292     
==========================================
+ Hits          286      537     +251     
- Misses        133      171      +38     
- Partials        8       11       +3     

Flag	Coverage Δ
unittests	74.68% <84.76%> (+7.70%)	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
pisa-controller/pkg/proxy/server.go	20.00% <0.00%> (-2.23%)	⬇️
pisa-controller/pkg/webhook/server.go	26.66% <0.00%> (ø)
pisa-controller/pkg/proxy/http.go	51.35% <44.11%> (-6.55%)	⬇️
pisa-controller/pkg/webhook/injection.go	59.02% <82.56%> (+20.08%)	⬆️
pisa-controller/pkg/proxy/builder.go	94.13% <98.33%> (+2.91%)	⬆️

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