chore: make default workspace proxy editable (#7903)

* chore: add editing the default workspace proxy

coderd/database/queries/siteconfig.sql

@@ -1,3 +1,23 @@
+-- name: UpsertDefaultProxy :exec
+-- The default proxy is implied and not actually stored in the database.
+-- So we need to store it's configuration here for display purposes.
+-- The functional values are immutable and controlled implicitly.
+INSERT INTO site_configs (key, value)
+VALUES
+    ('default_proxy_display_name', @display_name :: text),
+    ('default_proxy_icon_url', @icon_url :: text)
+ON CONFLICT
+    (key)
+DO UPDATE SET value = EXCLUDED.value WHERE site_configs.key = EXCLUDED.key
+;
+
+-- name: GetDefaultProxyConfig :one
+SELECT
+	COALESCE((SELECT value FROM site_configs WHERE key = 'default_proxy_display_name'), 'Default') :: text AS display_name,
+	COALESCE((SELECT value FROM site_configs WHERE key = 'default_proxy_icon_url'), '/emojis/1f3e1.png') :: text AS icon_url
+;
+
+
 -- name: InsertDeploymentID :exec
 INSERT INTO site_configs (key, value) VALUES ('deployment_id', $1);