fix: use consistent cert dir between certgen and standalone run

[mathetake]

What type of PR is this?

Fixes an inconsistency described in #7225 (comment) which makes the stanalone default mode works as expected.

What this PR does / why we need it:
This fixes the inconsistency between the dir where cergen generates certs vs the dir standalone mode expects to see TLS certs when no dir specifying env vars are not present, notably default behavor.

Which issue(s) this PR fixes:
N/A

Release Notes:No

[mathetake]

cc @arkodg @zirain

[mathetake]

this is the actual fix which makes this match with

// CertDir returns the certificate directory path (under ConfigHome).
func (p *Paths) CertDir(component string) string {
	return filepath.Join(p.ConfigHome, "certs", component)
}

[codecov]

Codecov Report

❌ Patch coverage is 44.44444% with 5 lines in your changes missing coverage. Please review.
✅ Project coverage is 72.00%. Comparing base (01b2ebf) to head (d3addc0).
⚠️ Report is 4 commits behind head on main.

Files with missing lines	Patch %	Lines
internal/cmd/certgen.go	44.44%	5 Missing ⚠️

❌ Your patch status has failed because the patch coverage (44.44%) is below the target coverage (60.00%). You can increase the patch coverage or adjust the target coverage.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #7351      +/-   ##
==========================================
- Coverage   72.05%   72.00%   -0.05%     
==========================================
  Files         230      230              
  Lines       33379    33379              
==========================================
- Hits        24050    24036      -14     
- Misses       7583     7595      +12     
- Partials     1746     1748       +2     

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[jukie]

/retest

[codefromthecrypt]

thanks