Allow `type: 'unknown'` in our Configuration schema

[dotNomad]

This PR does two things:

• Adds type = 'unknown' to our schema making it a valid option in our Configuration files
• Allows changing the type from unknown to something else and re-deploying
  • Changing types if the previous type is not unknown is still invalid

Consequences of this PR

With type = 'unknown' now passing schema validation for our Configuration files, when Config has that type:

• We lose the sidebar warning showing the user that the config is in error
• We lose TOML validation warnings if the user is using an extension like Even Better TOML
• Actions like including or excluding files can now be done
  • This addresses the trade off introduced in #2422 where .posit files couldn't be added automatically to the generated config with type = 'unknown'
• When deploying the content, it now gets created on Connect, as opposed to failing a pre-check in Publisher. Connect communicates that failure with "“Cannot process manifest: Unrecognized app mode”"
  • This can be addressed by the user by changing the type to something that produces a valid App Mode (anything but unknown) and re-deploying due to the 2nd change mentioned above

Intent

Further addresses #2419 and allows more actions on the Configuration file from sidebar when the Configuration type = 'unknown'

Type of Change

• [x] Refactor

Automated Tests

I did add an automated test to check that moving from App Mode "" (or type = 'unknown') to a valid App Mode was acceptable in our deployment pre-checks.