Make LDAP user update support adding sk-* format SSH keys

What does this MR do and why?

• When LDAP users perform auth-related actions like signing in, the code syncs user data between the LDAP server and GitLab.
• This includes adding SSH keys from the LDAP server to GitLab, if the sync feature is enabled.
• sk-* type SSH keys (security keys) were not syncing because the code only supports non-sk-* keys

This MR updates the LDAP sync logic to support adding sk-* keys during sync.

Alternatives

The fix is low-impact and purely additive: make the existing regex also match on sk-* keys, optionally. This ensures this fix won't break anything else or have unintended side effects

I considered a couple other options:

1. Make the regex filter only on key types supported in SSHPublicKey::TECHNOLOGIES list
2. Don't filter at all, and let the Key model validation fail adding any non-supported keys

I decided against these because:

• They are larger changes that could have side effects.
• Requires more detailed testing and manual testing.
• Changes more behaviour than just fixing the sk-* bug.
• I'm not against implementing either of the alternatives but I'd suggest doing them separately from fixing this bug.

References

Issue: #415363

How to set up and validate locally

1. Follow these instructions to validate locally
2. The above instructions verify that sk-* keys will be supported. To check that other non-sk-* types of keys continue to be supported, just add a bunch of different keys in step 4) when changing john's entry on the LDAP schema. Example:

Add more keys for `john` in `frontend.example.com.ldif`

# frontend.example.com.ldif

...

dn: uid=john,ou=people,dc=example,dc=com
...
objectClass: ldapPublicKey
...
initials: JD
sshPublicKey: <key_from_issue_description>

dn: uid=mary,ou=people,dc=example,dc=com
objectClass: inetOrgPerson
objectClass: posixAccount
objectClass: shadowAccount
objectClass: ldapPublicKey
...
initials: JD
sshPublicKey: sk-ssh-ed25519@openssh.com AAAAGnNrLXNzaC1lZDI1NTE5QG9wZW5zc2guY29tAAAAIPnI5pgZCsItcMh9e4lVK3CBP7cU0RbYnDzFE73dtdQnAAAABHNzaDo=
sshPublicKey: sk-ssh-ed25519@openssh.com AAAAGnNrLXNzaC1lZDI1NTE5QG9wZW5zc2guY29tAAAAIPnI5pgZCsItcMh9e4lVK3CBP7cU0RbYnDzFE73dtdQnAAAABHNzaDo= fake@email.com
sshPublicKey: ssh-ed25519 AAAAC3NzaC1lZDI1NTE5AAAAIETnVTgzqC1gatgSlC4zH6aYt2CAQzgJOhDRvf59ohL6 fake@email.com
...

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Related to #415363