Add spa_json_begin_array/object to replace
spa_json_init+spa_json_begin_array/object
This function is better because it does not waste a useless spa_json
structure as an iterator. The relaxed versions also error out when the
container is mismatched because parsing a mismatched container is not
going to give any results anyway.
Since `spa/utils/cleanup.h` is not a private header anymore, there is
no need for a separate `pipewire/cleanup.h` since the definitions of
the cleanup routines can now be moved into the respective headers.
Add a new config section that can contain a set of commands to run after
starting.
There is only load-module available now but it can be used to remove the
dependency on pactl when starting the server.
