fix: Add changelog for LDAP

Better late than never.

changelogs/unreleased/support-ldap-authentication.md

+## feat/box
+
+This authentication method doesn't store any secrets; instead,
+we delegate the whole auth to a pre-configured LDAP server. In
+the method's implementation, we connect to the LDAP server and
+perform a BIND operation which checks user's credentials.
+
+Usage example:
+
+```lua
+-- Set the default auth method to LDAP and create a new user.
+-- NOTE that we still have to provide a dummy password; otherwise
+-- box.schema.user.create will setup an empty auth data.
+box.cfg({auth_type = 'ldap'})
+box.schema.user.create('demo', { password = '' })
+
+-- Configure LDAP server connection URL and DN format string.
+os = require('os')
+os.setenv('TT_LDAP_URL', 'ldap://localhost:1389')
+os.setenv('TT_LDAP_DN_FMT', 'cn=$USER,ou=users,dc=example,dc=org')
+
+-- Authenticate using the LDAP authentication method via net.box.
+conn = require('net.box').connect(uri, {
+    user = 'demo',
+    password = 'password',
+    auth_type = 'ldap',
+})