ZEVA2 - task - zev unit transfer comments

**Describe the task**
In zeva1, credit transfer comments are associated with credit transfer history objects. This makes sense for certain comments made by a supplier when they perform certain actions (e.g. rescind a transfer, reject a transfer, etc.). However, it doesn't really make sense for government comments that are not associated with certain actions, but are associated with the transfer itself (having a look at the UIs associated with the transfer process should make this more apparent).

Currently, in zeva2, all comments are associated with a history entry; we should make it so that this continues to be the case for supplier comments, but gov comments are stored in their own separate table and associated with transfers themselves.

**Purpose**
This makes more sense; I believe that, in zeva1, the gov comment feature was added after the supplier comment feature, and so the gov comment feature inherited some legacy characteristics.

**Acceptance Criteria**
- [ ] Make a table that can store government zev unit transfer comments
- [ ] Create/update actions that allow government users to make/edit comments independent of other actions
- [ ] Create/update client components that facilitate the execution of the above actions
- [ ] Update the seed.ts file so that gov comments are copied over to the new table

**Additional context**
- There was a previous commit in zeva2 that stored all zev unit transfer comments in their own table; the code in there may be useful.