feat(sequence): add group sequence implementation

[Mulavar]

What this PR does:
add group sequence implementation.

Which issue(s) this PR fixes:

ref #94

Special notes for your reviewer:

Does this PR introduce a user-facing change?:

[codecov-commenter]

Codecov Report

Merging #400 (57346ec) into master (e947693) will decrease coverage by 1.41%.
The diff coverage is 5.10%.

@@            Coverage Diff             @@
##           master     #400      +/-   ##
==========================================
- Coverage   39.61%   38.20%   -1.42%     
==========================================
  Files         110      118       +8     
  Lines       14738    15662     +924     
==========================================
+ Hits         5839     5983     +144     
- Misses       8183     8932     +749     
- Partials      716      747      +31     

Impacted Files	Coverage Δ
pkg/sequence/group/group.go	7.96% <5.10%> (ø)
pkg/config/api.go	83.33% <0.00%> (-16.67%)	⬇️
pkg/config/file/file.go	74.26% <0.00%> (-15.21%)	⬇️
pkg/runtime/rule/shard_expr.go	78.94% <0.00%> (-9.29%)	⬇️
pkg/boot/discovery.go	57.10% <0.00%> (-8.31%)	⬇️
pkg/runtime/optimize/dml/select_scanner.go	70.63% <0.00%> (-6.38%)	⬇️
pkg/config/model.go	25.61% <0.00%> (-3.36%)	⬇️
pkg/runtime/rule/shard_expr_parse.go	82.35% <0.00%> (-3.02%)	⬇️
pkg/runtime/ast/show.go	32.99% <0.00%> (-2.92%)	⬇️
pkg/config/nacos/nacos.go	34.67% <0.00%> (-2.73%)	⬇️
... and 23 more

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[jjeffcaii]

pls add ut