Implement grouping options for the email type

[kgodey]

Problem

Users may want to group records that contain email types by first character or domain of the email value.

We need to provide the ability to group by these.

Solution

We should extend our record grouping mechanism to accept first character or domain as grouping parameters for columns of email types.

This involves:

• Implementing the grouping in the backend
• Updating the /api/v0/databases/<id>/types/ endpoint to store available grouping on this type

Additional context

• Please see these PRs for code related to grouping:
  • Record grouping #315
  • Fix grouping counts #353
• Grouping by first character is also a requirement for Implement grouping for Text types. #408 and implementation should be coordinated.
• Update filtering issues to cover storing filter/group information in the backend. #557 provides some context on storing groups.