Add a last updated timestamp to objects the plugin makes changes to

[sol1-matt]

Problem

While it may be possible to determine when the plugin last changed a object using the change log, as opposed to a user changing a object. It is not trivial for users to get a list of objects the plugin changed and the last change date of each object from the changelog.

Solution

Add a date based custom field to all objects that the plugin updates and update that field each time the plugin makes a change to the object.
This will allow easy filtering of objects by object type for when the plugin last updated that object, it also shows this value in the UI for each object.

name: something like promox_last_modified
object_types: all the ones the plugin modifies
group_name: Promox Plugin
type: value: datetime, label: Date & time