Add Python 3.10 support and drop Python 3.6 support

[sbethur]

• This contribution adheres to CONTRIBUTING.md.

• I've updated CHANGELOG.md if applicable.

- [ ] I've added tests applicable for this pull request

What does this Pull Request accomplish?

• Add support for Python 3.10
• Drop support for Python 3.6

List issues fixed by this Pull Request below, if any.

None

What testing has been done?

PR build

[sbethur]

The system tests will fail until internal PR 344267 is submitted.

[sbethur]

The system tests will fail until internal PR 344267 is submitted.

Well, the system tests on 3.10 got skipped rather than the PR build pipeline failing. Guess that's ok.

[sbethur]

The system tests will fail until internal PR 344267 is submitted.

Well, the system tests on 3.10 got skipped rather than the PR build pipeline failing. Guess that's ok.

The internal PR was submitted and the updated nimibot VM has been deployed. @marcoskirsch / @ni-jfitzger , this PR is ready for merge.

[ni-jfitzger]

The win_32 run failed on setting up for python 3.10 testing, but succeeded on all other Python versions in a previous run. RHEL and win_64 nimibot runs succeeded on all Python versions.

The win_32 failure appears to be a failure to install scipy due to No win32 wheel for Python 3.10.

[marcoskirsch]

Created #1811

[marcoskirsch]

@sbethur #1817 is merged (thanks @ni-jfitzger !).
Merge that and try again.

[sbethur]

@sbethur #1817 is merged (thanks @ni-jfitzger !). Merge that and try again.

Done. The PR build is running.