Skip automigrating for existing tables

[lpoli]

Fixes

This PR add version table so that we can later on migrate tables and its data based on this information.
Also, the automigration will drop tables only if automigration: true, default value is false.

[cnlangzi]

I don't how it works if a table is configured as keep_tables on yaml file, and there are new columns should be added, or some old columns should be dropped. let's waiting for @peterlimg to review

[codecov-commenter]

Codecov Report

Merging #705 (1ad68de) into staging (2132c7d) will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff            @@
##           staging     #705   +/-   ##
========================================
  Coverage    24.06%   24.06%           
========================================
  Files           69       69           
  Lines         7957     7957           
========================================
  Hits          1915     1915           
  Misses        5757     5757           
  Partials       285      285           

Flag	Coverage Δ
Unit-Tests	24.06% <ø> (ø)

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[cnlangzi]

I think you have some misunderstand about AutoMigrate on schema. why a table has to be dropped before migrating its schema? nobody will drop table to loss all data when it is migrated. I can't understand your idea.

[cnlangzi]

LGTM

[service-0chain]

Manual system tests [success] with the following config

config	value
tests skipped	FALSE
system-tests	master
gosdk	NOT OVERRIDDEN
zboxcli	staging
zwalletcli	staging
0chain	staging
blobber	fix/automigrate-existing-table-issue
authorizer	staging
0box	staging
0block	staging
0dns	staging
explorer	master
0proxy	staging
0search	staging