[BUG] Nested role resolution crashes on malformed DN instead of gracefully skipping

[charleshawkins1-byte]

When resolve_nested_roles: true and a user belongs to a group with an invalid DN
containing escape sequences (e.g., \0A newline), the nested resolution throws
INVALID_DN_SYNTAX followed by NullPointerException, causing the entire role
lookup to fail and return empty backend_roles.

Expected behavior: Skip malformed DNs and continue processing valid groups.

Affected version: OpenSearch 3.x
Error:

• INVALID_DN_SYNTAX: CN=SCA-LDAP\0ACNF:...
• NullPointerException: Cannot invoke "org.ldaptive.LdapEntry.getAttribute(String)" because "e0" is null

Stack trace:
at org.opensearch.security.auth.ldap.backend.LDAPAuthorizationBackend.resolveNestedRoles
at org.opensearch.security.auth.ldap.backend.LDAPAuthorizationBackend.addRoles

[krisfreedain]

@DarshitChanpura @cwperks @derek-ho @RyanL1997 @nibix maintainers please take a look

Catch All Triage - 1 2