Docs - Updated documentation to reflect that v4 of the provider is now released

[bubbletroubles]

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Description

PR Checklist

• I have followed the guidelines in our Contributing Documentation.
• I have checked to ensure there aren't other open Pull Requests for the same update/change.
• I have checked if my changes close any open issues. If so please include appropriate closing keywords below.
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  For example: “resource_name_here - description of change e.g. adding property new_property_name_here”

Documentation

The documentation detailed the "upcoming" release of AzureRM v4.x. This is now released, so updated the docs to reflect that.