Drop support for python 3.6, add support for 3.10

[kevin-bates]

Since Python 3.6 is end-of-life and PR #6215 drops 3.6 from the CI matrices (while adding 3.10) we should do the same at an official compacity (updating the classifiers, etc.).

I'm assuming this is something that can be delivered within a minor release and have added a 6.5 milestone.

[JasonWeill]

@penguinolog Is your commit tested and known to fix this issue? If so, can you please create a pull request?

[penguinolog]

@penguinolog Is your commit tested and known to fix this issue? If so, can you please create a pull request?

PR is open and waiting for merge

[JasonWeill]

Tagging PR #6260 (appears to be blocked by #6213)

[penguinolog]

Tagging PR #6260 (appears to be blocked by #6213)

Formally not blocked - 1 python file intersection. But we miss CI for frontend part (stable fail looks not good)