Make identity_inputs optional

[allisonking]

Closes #2259

Code Changes

• Makes identity inputs optional in typescript
• Uses email as a default when no identity inputs are provided

Steps to Confirm

• Start up nox -s test_env. The privacy center should come up without problem, despite the test env's config not having identity inputs. Clicking on "manage your consent" should show only an email field.
• Editing the identity_inputs field on either actions or consent options should show the fields as you set them (note the test env's privacy center will not hot reload though—it's easiest to test this just with npm run dev, or to nox -s "build(privacy-center)" and then docker-compose up fides-pc --no-deps fides-pc

Pre-Merge Checklist

• All CI Pipelines Succeeded
• Documentation:
  • documentation complete, PR opened in fidesdocs
  • documentation issue created in fidesdocs
• Issue Requirements are Met
• Relevant Follow-Up Issues Created
• Update CHANGELOG.md

Description Of Changes

Write some things here about the changes and any potential caveats

[TheAndrewJackson]

💥

[allisonking]

The failing test is unrelated to this PR (it's happening in other PRs too 😕 )