feat: add flag to disable password auth (#5991)

Adds a flag --disable-password-auth that prevents the password login
endpoint from working unless the user has the "owner" (aka. site admin)
role.

Adds a subcommand `coder server create-admin-user` which creates a user
directly in the database with the "owner" role, the "admin" role in
every organization, and password auth. This is to avoid lock-out
situations where all accounts have the login type set to an identity
provider and nobody can login.

coderd/apidoc/docs.go

@@ -6012,6 +6012,9 @@ const docTemplate = `{
                 "derp": {
                     "$ref": "#/definitions/codersdk.DERP"
                 },
+                "disable_password_auth": {
+                    "$ref": "#/definitions/codersdk.DeploymentConfigField-bool"
+                },
                 "disable_path_apps": {
                     "$ref": "#/definitions/codersdk.DeploymentConfigField-bool"
                 },

coderd/apidoc/swagger.json

@@ -5343,6 +5343,9 @@
         "derp": {
           "$ref": "#/definitions/codersdk.DERP"
         },
+        "disable_password_auth": {
+          "$ref": "#/definitions/codersdk.DeploymentConfigField-bool"
+        },
         "disable_path_apps": {
           "$ref": "#/definitions/codersdk.DeploymentConfigField-bool"
         },