feat(operator): add mockgen cmd to makefile

[moomman]

Type of change:

• Bugfix
• New feature provided
• Improve performance
• Backport patches

What this PR does / why we need it:

add mockgen cmd

Pre-submission checklist:

• Did you explain what problem does this PR solve? Or what new features have been added?
• Have you added corresponding test cases?
• Have you modified the corresponding document?

#272

[sonarcloud]

Kudos, SonarCloud Quality Gate passed!   

0 Bugs
0 Vulnerabilities
0 Security Hotspots
0 Code Smells

No Coverage information
No Duplication information

[codecov-commenter]

Codecov Report

Merging #403 (3604a24) into main (e52f093) will decrease coverage by 7.63%.
The diff coverage is 12.11%.

@@            Coverage Diff             @@
##             main     #403      +/-   ##
==========================================
- Coverage   47.34%   39.71%   -7.63%     
==========================================
  Files          48       51       +3     
  Lines        5264     6083     +819     
==========================================
- Hits         2492     2416      -76     
- Misses       2547     3448     +901     
+ Partials      225      219       -6     

Impacted Files	Coverage Δ
pitr/agent/internal/handler/backup.go	15.00% <ø> (ø)
pitr/agent/internal/handler/restore.go	0.00% <ø> (ø)
pitr/agent/internal/handler/show.go	0.00% <ø> (ø)
pitr/agent/internal/pkg/opengauss.go	3.93% <ø> (ø)
pitr/agent/internal/pkg/pkg.go	0.00% <ø> (ø)
pitr/agent/pkg/cmds/cmd.go	49.46% <ø> (ø)
pitr/agent/pkg/gsutil/conn.go	29.41% <ø> (ø)
pitr/agent/pkg/strutil/rand_string.go	90.90% <ø> (ø)
pitr/agent/pkg/xerror/error.go	61.53% <ø> (ø)
pitr/cli/internal/cmd/backup.go	73.47% <0.00%> (ø)
... and 25 more

... and 2 files with indirect coverage changes

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