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.

site/src/api/typesGenerated.ts

@@ -327,6 +327,7 @@ export interface DeploymentConfig {
   readonly disable_path_apps: DeploymentConfigField<boolean>
   readonly max_session_expiry: DeploymentConfigField<number>
   readonly disable_session_expiry_refresh: DeploymentConfigField<boolean>
+  readonly disable_password_auth: DeploymentConfigField<boolean>
   readonly address: DeploymentConfigField<string>
   readonly experimental: DeploymentConfigField<boolean>
 }