* Split activity table into sent and received parts (fixes#3103)
The received activities are only stored in order to avoid processing
the same incoming activity multiple times. For this purpose it is
completely unnecessary to store the data. So we can split the
table into sent_activity and received_activity parts, where
only sent_activity table needs to store activity data. This should
reduce storage use significantly.
Also reduces activity storage duration to three months, we can reduce
this further if necessary.
Additionally the id columns of activity tables are removed because
they are completely unused and risk overflowing (fixes#3560).
* address review
* move insert_received_activity() methods to verify handlers
* remove unnecessary conflict line
* clippy
* use on conflict, add tests
