Support for content revisions

[stooit]

Description
Some web content may be revisionable by nature, and expose multiple versions of the same content. This may mean that content existing at multiple URLs can be tied to a single source entity so revisions of the same content can be created in the destination CMS.

Proposed solution

Additional context
Example: https://softwaredevelopers.ato.gov.au/node/100017647/revisions

[nickgeorgiou]

Similar to grouping, there needs to be a way to determine whether a page is a revision of another. Groups provides a good base for functionality that should be implemented. Possible criteria for determining whether something is a revision:

• Has an Element (like Migrate\Crawler\Group\Element)
• Matches a Path pattern (like Migrate\Crawler\Group\Path)
• Has an Element Value (like Migrate\Crawler\Group\Value)

Crawler\Revision should also extract the path/URL that the page is a revision of.