Handle deployment settings in a new collection in the database

[jdbocarsly]

We have a number of settings on the frontend and backend that are currently set using environement variables. It would be nice for admins to be able to set many of these settings from the app itself.

To do this, we will need a new database collection called "settings" (or similar), that holds a document with settings for the overall deployment, as well as documents for individual block types. Many of the settings in resources.js could be stored here, as well as things like API keys for llm models, configuration for login types, etc. These settings could be changeable by admins from the new admin panel that is in development.

[ml-evs]

Some stuff needed (in discussion with @BenjaminCharmes):

• Database collection for settings, with some distinction between public (values that the UI can access, e.g., logo URL, whether the inventory is editable) and private (secret keys, settable by admins but not reported by the API)
• API routes for returning public settings (e.g., /info/settings) and changing public and private settings /admin/settings
• Way of viewing and changing specific hard-coded settings (for now) in the admin dashboard
• App loading settings into store on first load

[ml-evs]

This general approach will be followed by #667 at some point too