pjsip realtime: increase the size of some columns

The string lengths on certain columns created through alembic for PJSIP were
too short. For instance, columns containing URIs are currently set to 40
characters, but this can be too small and result in truncated values.  Added
an alembic migration script that increases the size of these columns and a
few others to 255.

ASTERISK-23639 #close
Reported by: Mark Michelson
Review: https://reviewboard.asterisk.org/r/3475/
........

Merged revisions 412992 from http://svn.asterisk.org/svn/asterisk/branches/12


git-svn-id: http://svn.asterisk.org/svn/asterisk/trunk@412993 f38db490-d61c-443f-a65b-d21fe96a405b