Fix default value for modManagerLog.occurred column

[opengeek]

What does it do?

Adds a default value for the datetime column in the modx_manager_log table that is compatible with strict modes, which may be enabled in some environments.

Re-up of #15736 with migration

Why is it needed?

Beginning with MySQL > 5.7.8 added strict modes ERROR_FOR_DIVISION_BY_ZERO, NO_ZERO_DATE, NO_ZERO_IN_DATE. With these strict modes enabled, a datetime default value cannot be NULL and must be > '0000-00-00'.

How to test

Install/update on MySQL 5.7.8

Related issue(s)/PR(s)

Re-up of #15736 Backport of #16526