Fallible Settings (#42938)

Also tidies up error notifications so that in the case of syntax errors
we don't see noise about the migration failing as well.

Release Notes:

- Invalid values in settings files will no longer prevent the rest of
the file from being parsed.

Cargo.toml

@@ -641,7 +641,6 @@ serde_json_lenient = { version = "0.2", features = [
 serde_path_to_error = "0.1.17"
 serde_repr = "0.1"
 serde_urlencoded = "0.7"
-serde_with = "3.4.0"
 sha2 = "0.10"
 shellexpand = "2.1.0"
 shlex = "1.3.0"