docs: support docs for SAML session in Custom Login UI (#9144)

# Which Problems Are Solved

SAML session implemented, but no how-to comparable to the OIDC sessions
for custom login available.

# How the Problems Are Solved

Added documentation, which should be also comparable with the OIDC
session for ease-of-use.

# Additional Changes

Added generated SAML API docs.

# Additional Context

Closes #9088 
Follow-up issue #9267

---------

Co-authored-by: Fabienne Bühler <fabienne@zitadel.com>
Co-authored-by: Livio Spring <livio.a@gmail.com>

docs/docusaurus.config.js

@@ -308,6 +308,14 @@ module.exports = {
               categoryLinkSource: "auto",
             },
           },
+          saml_v2: {
+            specPath: ".artifacts/openapi/zitadel/saml/v2/saml_service.swagger.json",
+            outputDir: "docs/apis/resources/saml_service_v2",
+            sidebarOptions: {
+              groupPathsBy: "tag",
+              categoryLinkSource: "auto",
+            },
+          },
           settings_v2: {
             specPath: ".artifacts/openapi/zitadel/settings/v2/settings_service.swagger.json",
             outputDir: "docs/apis/resources/settings_service_v2",