chore: enable early-return and superfluous-else from revive

[mmorel-35]

Description

early-return: In Go it is idiomatic to minimize nesting statements, a typical example is to avoid if-then-else constructions.

superfluous-else: To improve the readability of code, it is recommended to reduce the indentation as much as possible. This rule highlights redundant else-blocks that can be eliminated from the code.

[codecov]

Codecov Report

Attention: Patch coverage is 52.94118% with 8 lines in your changes missing coverage. Please review.

Project coverage is 68.74%. Comparing base (ecd7cfc) to head (10d7cea).
Report is 6 commits behind head on main.

Files with missing lines	Patch %	Lines
server/etcdserver/api/v2store/store.go	33.33%	2 Missing and 2 partials ⚠️
etcdctl/ctlv3/command/check.go	0.00%	3 Missing ⚠️
etcdctl/ctlv3/ctl.go	0.00%	1 Missing ⚠️

Additional details and impacted files

Files with missing lines	Coverage Δ
pkg/flags/selective_string.go	100.00% <100.00%> (ø)
server/etcdserver/cluster_util.go	66.17% <100.00%> (-0.13%)	⬇️
server/proxy/grpcproxy/watcher.go	91.83% <100.00%> (-0.17%)	⬇️
server/storage/mvcc/watchable_store.go	93.89% <100.00%> (-0.02%)	⬇️
etcdctl/ctlv3/ctl.go	0.00% <0.00%> (ø)
etcdctl/ctlv3/command/check.go	0.00% <0.00%> (ø)
server/etcdserver/api/v2store/store.go	83.87% <33.33%> (-0.05%)	⬇️

... and 24 files with indirect coverage changes

@@            Coverage Diff             @@
##             main   #19152      +/-   ##
==========================================
- Coverage   68.76%   68.74%   -0.02%     
==========================================
  Files         420      420              
  Lines       35650    35641       -9     
==========================================
- Hits        24513    24500      -13     
+ Misses       9714     9706       -8     
- Partials     1423     1435      +12     

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[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: ahrtr, mmorel-35

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