#133: on ldap connection error, communicate 504

[dk1844]

This PR introduces different non-ok response to users besides the original 401, on LDAP connection errors.

In this particular situation, failing to connect to LDAP should give users 504.

Example run with mangled config to induce the error:

POST http://localhost:9090/token/generate?groups-prefixes=
with e.g. Authorization: Basic bXl1c2VybmFtZTp3aGF0LWFyZS15b3UtbG9va2luZy1mb3ItaGVyZT8=

->
504

{"error": "LDAP connection failed: LDAP connection issue: corp.bogus.com:636; nested exception is javax.naming.CommunicationException: corp.bogus.com:636 [Root exception is java.net.UnknownHostException: corp.bogus.com]"}

@TheLydonKing

Release notes:

• For LDAP connection errors, 504 error code is communciated to signify the state difference compared to previsouly present 504

Closes #133

[github-actions]

JaCoCo code coverage report - scala:2.12.17

File	Coverage [58.1%]	❌
AuthManagerConfig.scala	96.88%	🍏
SecurityConfig.scala	88.37%	🍏
JWTService.scala	82.77%	🍏
RestResponseEntityExceptionHandler.scala	62.71%	❌
ActiveDirectoryLDAPAuthenticationProvider.scala	51.32%	❌
LdapUserRepository.scala	21.53%	❌
KerberosFailureHandler.scala	0%	❌
KerberosSPNEGOAuthenticationProvider.scala	0%	❌
LdapConnectionException.scala	0%	❌

Total Project Coverage	68.84%	🍏

[dk1844]

LGTM

[TheLydonKing]

LGTM and tested on my side

[dk1844]

LGTM