rename setting to allow_multiple_connections_per_peer_id

[milahu]

fix #8215 (comment)

not tested, feeling lucky : P

basically this is

rg -l allow_multiple_connections_per_pid |
xargs sed -i -E 's|(allow_multiple_connections_per)_pid|\1_peer_id|g'

git mv simulation/test_allow_multiple_connections_per_{pid,peer_id}.cpp

why?

• make it consistent with the rest of the codebase: duplicate_peer_id etc
• pid is okay for a local variable, but bad in a user-facing API

[arvidn]

was this released in the last release from 2.0.x? I was released in 2.1rc1, but that's probably fine to change. This is user facing so if it has been released we need to just add an alias

[arvidn]

if the existing name has not been included in a release yet, I think this change is reasonable.