realtime: Create extensions in alembic ast-db-manage contribution
When the alembic scripts were written for creating Asterisk
realtime databases the extensions table for dialplan wasn't
included. This update creates the extensions table.
(closes issue ASTERISK-22815)
Reported by: Zone Conkle
Review: https://reviewboard.asterisk.org/r/3064/
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Merged revisions 403713 from http://svn.asterisk.org/svn/asterisk/branches/12
git-svn-id: https://origsvn.digium.com/svn/asterisk/trunk@403714
65c4cc65-6c06-0410-ace0-
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