server: Add APIs for RawKV GC

[AmoebaProtozoa]

Signed-off-by: AmoebaProtozoa [email protected]

What problem does this PR solve?

Add APIs for RawKV GC (client part of #4866).
Issue Number: ref #4865
RFC: tikv/rfcs#90

What is changed and how does it work?

Add APIs for RawKV GC.

Check List

Tests

• Manual tests with server

Code changes

• Has configuration change
  No
• Has HTTP API interfaces changed (Don't forget to add the declarative for the new API)
  No
• Has persistent data change
  No

Side effects
No

Release note

Add APIs for RawKV GC.

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[codecov]

Codecov Report

Merging #5138 (90c9360) into master (b100049) will decrease coverage by 0.21%.
The diff coverage is 50.47%.

@@            Coverage Diff             @@
##           master    #5138      +/-   ##
==========================================
- Coverage   75.65%   75.44%   -0.22%     
==========================================
  Files         310      312       +2     
  Lines       30675    30959     +284     
==========================================
+ Hits        23208    23357     +149     
- Misses       5463     5579     +116     
- Partials     2004     2023      +19     

Flag	Coverage Δ
unittests	75.44% <50.47%> (-0.22%)	⬇️

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

Impacted Files	Coverage Δ
client/gc_client.go	0.00% <0.00%> (ø)
client/metrics.go	100.00% <ø> (ø)
tests/cluster.go	79.59% <25.00%> (-0.75%)	⬇️
server/storage/kv/etcd_kv.go	69.56% <46.42%> (-10.15%)	⬇️
client/client.go	68.54% <60.00%> (+0.02%)	⬆️
server/storage/endpoint/gc_key_space.go	70.00% <71.42%> (+3.33%)	⬆️
server/gc_service.go	74.02% <74.02%> (ø)
pkg/testutil/testutil.go	93.93% <100.00%> (+0.60%)	⬆️
server/server.go	74.30% <100.00%> (-0.77%)	⬇️
server/storage/endpoint/key_path.go	100.00% <100.00%> (ø)
... and 28 more

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[ti-chi-bot]

@AmoebaProtozoa: PR needs rebase.

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