fix: 'readyz' enpdoint check only required service

The readyz endpoint contained unconditional checks for the LDAP and nats
endpoints. Depending on configuration neihter LDAP nor NATS might be
required.
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Internal Server Error - Gitea: Git with a cup of tea
500 Internal Server Error

Gitea Version: 1.28.0+dev-477-g8b6ad49a5f