Refactor: Move cert reloader to pkg/crt/reloader.go

[coderabbitai]

Summary

Move and rename the TLS certificate reloader from server/common/certreloader.go to pkg/crt/reloader.go for better package organization and naming clarity.

Background

Suggested in PR #700 (#700) by @bartoszmajsak in review comment #700 (comment).

Requested as a follow-up issue by @pierDipi.

Changes Required

• Create new package pkg/crt
• Move server/common/certreloader.go → pkg/crt/reloader.go
• Update package declaration from package common to package crt
• Update all import paths referencing the old location across the server/ directory
• Move corresponding test file server/common/certreloader_test.go → pkg/crt/reloader_test.go