Add a provider support matrix

[agrare]

The CFME docs have a section for what versions of providers are supported for each release of CFME. This would be helpful to have for ManageIQ as well.

[agrare]

cc @Fryguy @dmetzger57

[Fryguy]

Is this the same as the capabilities matrix we have in documentation now? If so can this be closed?

[agrare]

@Fryguy slightly different, this is about which versions of the provider do we support, e.g.:

Provider      Versions
-------- | --------------
VMware   | 5.5 6.0 6.5 6.7
RHV      | 4.2 4.3
OSP      | 15 16

To indicate for example older than vSphere 5.5 is not supported and vSphere 7.0 is not supported (just an example)

[chessbyte]

We should be careful with the language here. Maybe “known to work with” or “community verified on”, but not “supported”