Implement HearingDay model to represent virtual hearing

[rubaiyat22]

Description

The current HearingDay model looks as follows:

HearingDay(
  id: integer,
  bva_poc: string,
  created_at: datetime,
  created_by_id: integer,
  deleted_at: datetime,
  judge_id: integer,
  lock: boolean,
  notes: text,
  regional_office: string,
  request_type: string,
  room: string,
  scheduled_for: date,
  updated_at: datetime,
  updated_by_id: integer
)

All of the above fields should be sufficient for a virtual hearing day. All fields except room should be relevant to track for a virtual hearing day since virtual hearings won't have room associated with them.

Currently, the HearingDayAddModal has a checkbox to indicate whether not to assign rooms for hearings (which is checked by default)

HearingDayController uses the param assign_room to determine whether to assign rooms. We can ignore room assignment completely and bypass it here. The room field can stay nil for virtual hearing days.

Acceptance criteria

• ensure existing tests pass and existing functionality remains unbroken
• write unit tests for HearingDayController and HearingDay model

Background/context/resources

• Research: new hearing type of virtual
  

Technical notes

• All of our request types are stored as single character here and V is taken by video, we may need to break convention and store virtual as VIRTUAL
• There's some calculation for generating hearing day schedule where room is taken into account. We might need to look deeper and see if virtual hearing days will be compatible for this.