Update HelmRepository, OCIRepository, and Bucket documentation to use
"Mutual TLS Authentication" section titles instead of "Cert secret
reference". This improves discoverability of mTLS capabilities and
follows GitRepository's established pattern.
The previous generic titles obscured mutual TLS functionality, causing
users to miss this important security feature. Updated descriptions
explicitly mention mutual TLS authentication while maintaining all
existing YAML examples and technical accuracy.
Signed-off-by: cappyzawa <cappyzawa@gmail.com>
cappyzawa