NMS-16316: Auto update eventconf from overlay events

[mmahacek]

This is planned for after #7028 merges. That PR provides some placeholders in select config files as both a operator note and scripting placeholder.

This PR updates the core container entrypoint.sh script to update eventconf.xml and syslog config based on any files in the overlay events/syslog directories. If the user provides a customized eventconf/syslog config that doesn't include the placeholder comments, this script will skip over and make no changes.

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External References

• Jira (Issue Tracker): https://opennms.atlassian.net/browse/NMS-16316