Migrate from pytz

[MartinHjelmare]

Breaking change

Proposed change

• Remove pytz requirement and use standard library for creating timezone aware UTC datetime from timestamp.
  • https://pytz-deprecation-shim.readthedocs.io/en/latest/migration.html
• Bump tzlocal to 4.0+ and use get_localzone_name to get the local timezone name.
  • https://pypi.org/project/tzlocal/

Type of change

• Dependency upgrade
• Bugfix (non-breaking change which fixes an issue)
• New service (thank you!)
• New feature (which adds functionality to an existing service)
• Breaking change (fix/feature causing existing functionality to break)
• Code quality improvements to existing code or addition of tests
• Documentation or code sample

Example of code:

Additional information

• This PR fixes or closes issue: fixes #
• This PR is related to issue:

Checklist

• The code change is tested and works locally.
• Local tests pass. Your PR cannot be merged unless tests pass
• There is no commented out code in this PR.
• Tests have been added to verify that the new code works.

If user exposed functionality or configuration variables are added/changed:

• Documentation added/updated to README