Ensure minimum maxSets is at least one

[theodoregoetz]

Following the discussions in #960 and #961 this sets the minimum maxSets to 1 so that when switching out graphics pipelines that use different descriptor sets, the warning about Context::reserve() is avoided. See also

See issues:

• #960
• #961

And in vsgExamples:

• https://github.com/vsg-dev/vsgExamples/issues/312
• https://github.com/vsg-dev/vsgExamples/pull/311

This PR is a possible fix for the warning, but it's unclear to this author if this is the correct and robust solution. I expect a discussion on the merits of this w.r.t. other possible changes to follow here or in the discussion board.