chore: add oidc redirect url to override access url (#21521)

If a deployment has 2 domains, overriding the oidc url allows the oidc
redirect to differ from the access_url

response to https://github.com/coder/coder/discussions/21500

**This config setting is hidden by default**

coderd/apidoc/docs.go

@@ -16784,6 +16784,14 @@ const docTemplate = `{
                 "organization_mapping": {
                     "type": "object"
                 },
+                "redirect_url": {
+                    "description": "RedirectURL is optional, defaulting to 'ACCESS_URL'. Only useful in niche\nsituations where the OIDC callback domain is different from the ACCESS_URL\ndomain.",
+                    "allOf": [
+                        {
+                            "$ref": "#/definitions/serpent.URL"
+                        }
+                    ]
+                },
                 "scopes": {
                     "type": "array",
                     "items": {

coderd/apidoc/swagger.json

@@ -15248,6 +15248,14 @@
 				"organization_mapping": {
 					"type": "object"
 				},
+				"redirect_url": {
+					"description": "RedirectURL is optional, defaulting to 'ACCESS_URL'. Only useful in niche\nsituations where the OIDC callback domain is different from the ACCESS_URL\ndomain.",
+					"allOf": [
+						{
+							"$ref": "#/definitions/serpent.URL"
+						}
+					]
+				},
 				"scopes": {
 					"type": "array",
 					"items": {