List the supported versions of grafana

[bg451]

Our plug in should be compatible with the latest patch of each minor release.

Versions tested so far

• 5.3.1
• 5.2.3
• 5.1.5
• 5.0.4
• 4.6.4

[miry]

Pls add v6.6.2 to the list

[miry]

In grafana 7 it has the problem to setup Options for query.