Documentation: restructure connector docs to a single folder

Documentation/authproxy.md

Documentation/connectors/authproxy.md

Documentation/connectors/github.md

Documentation/connectors/gitlab.md

Documentation/connectors/ldap.md

Documentation/connectors/linkedin.md

Documentation/connectors/microsoft.md

Documentation/connectors/oidc.md

Documentation/connectors/saml.md

Documentation/github-connector.md

Documentation/gitlab-connector.md

Documentation/ldap-connector.md

Documentation/linkedin-connector.md

Documentation/microsoft-connector.md

Documentation/oidc-connector.md

Documentation/saml-connector.md

README.md