1. Updating table name to be more readable.
2. Adding a column with status.

Note 1:
This table is empty in the current state so it's safe to just drop and create.

Note 2:
With the current design, we allow for ciphertext to be the empty string. This is the case when we need to send something to a peer but olm session not exist or is malformed. The alternative is making this field nullable, but this will make implementation more complex and will require a lot of additional code (mostly because of ENG-5719) so going for the empty string when ciphertext is missing.

Note 3:
We need a bit different API to this table - updated in the next diffs along with tests.

Depends on D12047

1. Migration succeeded.
2. Creating DB from scratch works.
3. Tests