E2E room keys table duplicate error

*This issue was originally created by [**@kegsay**](https://github.com/kegsay) at .*

```
an 15 03:57:49 matrix postgres[22977]: 2022-01-15 03:57:49.886 UTC [22977] ERROR: duplicate key value violates unique constraint "e2e_room_keys_idx"
Jan 15 03:57:49 matrix postgres[22977]: 2022-01-15 03:57:49.886 UTC [22977] DETAIL: Key (user_id, room_id, session_id, version)=(@real-changeling:hisp>
Jan 15 03:57:49 matrix postgres[22977]: 2022-01-15 03:57:49.886 UTC [22977] STATEMENT: INSERT INTO account_e2e_room_keys(user_id, room_id, session_id,>
Notice: journal has been rotated since unit was started, output may be incomplete.
```

For table:
```sql
CREATE TABLE IF NOT EXISTS account_e2e_room_keys (
user_id TEXT NOT NULL,
room_id TEXT NOT NULL,
session_id TEXT NOT NULL,

version TEXT NOT NULL,
first_message_index INTEGER NOT NULL,
forwarded_count INTEGER NOT NULL,
is_verified BOOLEAN NOT NULL,
session_data TEXT NOT NULL
);
CREATE UNIQUE INDEX IF NOT EXISTS e2e_room_keys_idx ON account_e2e_room_keys(user_id, room_id, session_id, version);
CREATE INDEX IF NOT EXISTS e2e_room_keys_versions_idx ON account_e2e_room_keys(user_id, version);
```

So in other words the client is uploading the same key backup twice. This is probably possible if there are network errors on the request to upload keys. Feels like an easy fix with a Complement regression test.

Start with the account_e2e_room_keys schema and the end-to-end key-upload path, then reproduce the duplicate upload with a Complement regression test. Done means retrying the same key upload no longer causes the e2e_room_keys_idx duplicate-key error and the regression test passes.

Written by the indexing model from the issue text.