test: add unit tests for LDAP authentication strategy

Test cases cover: successful auth with admin/non-admin roles,
user not found, user group rejection, invalid password,
connection errors, multiple entries in search result,
missing credentials, and escapeFilterValue with normal strings,
LDAP injection attempts, and RFC 4515 special characters.

Signed-off-by: Kwangjin Ko <kyet@me.com>

Author: 1saac-k