Auto merge of #3994 - Turbo87:read-only, r=locks

site_metadata: Expose `read_only` field

As discussed on Thursday, it would be nice to display on the frontend that we're currently in read-only mode during e.g. database updates. This PR adds a `read_only` field to the `/api/v1/site_metadata` endpoint response.

Author: bors

src/controllers/site_metadata.rs

@@ -5,11 +5,15 @@ use super::prelude::*;
 /// The sha is contained within the `HEROKU_SLUG_COMMIT` environment variable.
 /// If `HEROKU_SLUG_COMMIT` is not set, returns `"unknown"`.
 pub fn show_deployed_sha(req: &mut dyn RequestExt) -> EndpointResult {
+    let config = &req.app().config;
+    let read_only = config.db.are_all_read_only();
+
     let deployed_sha =
         dotenv::var("HEROKU_SLUG_COMMIT").unwrap_or_else(|_| String::from("unknown"));
 
     Ok(req.json(&json!({
         "deployed_sha": &deployed_sha[..],
         "commit": &deployed_sha[..],
+        "read_only": read_only,
     })))
 }