fix mian.py: make start delay configureable

[s-grechkin]

I got a problem with tg bot in docker container on extra orange-pi host.
I did not get greeting message, also no timelapses and status messages. Status command sent only snapshot.
After startup I got error message ''appscheduler Run time of job start_scheduler <...> was missed by <...>.
Also I noticed that time between adding this job and other messages in log is more than 5 seconds.
Python-telegram-bot docs says that run_polling method starts its own scheduler and first job in queue is start_scheduler callback.
So core of problem is time of strating bot (in run_polling method) is more than delay in run_once call parameters.

[s-grechkin]

10 seconds delay caused stable work for me

[KapJI]

I feel like this masks symptom instead of fixing the real issue. It needs to be investigated why this happens, not just increasing startup delay.