docs: Add LDAP Authentik and fix references to certificates endpoint

[akram09]

This Pull Request adds authentic ldap how to guide and updates the documentation to fix cases assuming only one certificate endpoint. For example juju integrate opensearch self-signed-certificates => juju integrate opensearch:certificates self-signed-certificates

[Copilot]

🟡 Changes recommended

The LDAP guide documents unsupported charm configuration and endpoints, plus commands that will fail as written.

2 open issues

• Documented LDAP config options are undeclared · New
• Documented LDAP integrations use undeclared relation endpoints · New

What changed in this PR

Adds LDAP authentication guidance for Authentik and GLAuth, while correcting Juju TLS certificate endpoint references.

Changes:

• Updates certificate integration commands across documentation.
• Adds and indexes the LDAP authentication guide.
• Adds LDAP provider names to the custom wordlist.

File	Summary
README.md	Updates TLS relation commands.
docs/​tutorial/​3-enable-encryption.md	Updates certificate integration syntax.
docs/​index.md	Adds LDAP security documentation.
docs/​how-to/​tls-encryption.md	Updates TLS integration syntax.
docs/​how-to/​perform-load-testing.md	Updates TLS setup commands.
docs/​how-to/​index.md	Adds LDAP guide navigation.
docs/​how-to/​enable-ldap-authentication.md	Adds LDAP setup guidance, but includes unsupported configuration, relations, and commands.
docs/​how-to/​deploy/​large.md	Updates TLS relations for large deployments.
docs/​how-to/​access-using-oauth.md	Updates certificate endpoint usage.
docs/​contributing.md	Updates development TLS commands.
docs/​.custom_wordlist.txt	Adds LDAP provider names.

_{Review effort: Lite}