Add backend logic for saving queries with custom codes

[nickclyde]

Description:

Right now our "query_data" column contains a JSON object with condition IDs for keys. For custom codes we will likely need to add a new key eg "custom" which lists additional value sets attached to the query

Acceptance Criteria:

• There is new backend logic which allows saving queries with custom codes
• We need a dummy condition called "custom" or something like that, which all new valuesets will be tied to

[linear]

QUE-235 Add backend logic for saving queries with custom codes