Resolve datetime deprecation warnings

[emmanuel-ferdman]

Description

This small PR resolves the deprecation warnings on datetime in Python3.12+. You can find them in the CI logs:

  /home/runner/work/opentelemetry-python-contrib/opentelemetry-python-contrib/exporter/opentelemetry-exporter-richconsole/src/opentelemetry/exporter/richconsole/__init__.py:71: DeprecationWarning: datetime.datetime.utcfromtimestamp() is deprecated and scheduled for removal in a future version. Use timezone-aware objects to represent datetimes in UTC: datetime.datetime.fromtimestamp(timestamp, datetime.UTC).
    ts = datetime.datetime.utcfromtimestamp(nanoseconds / 1e9)

Type of change

Please delete options that are not relevant.

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• This change requires a documentation update

How Has This Been Tested?

run tests

Does This PR Require a Core Repo Change?

• Yes. - Link to PR:
• No.

Checklist:

See contributing.md for styleguide, changelog guidelines, and more.

• Followed the style guidelines of this project
• Changelogs have been updated
• Unit tests have been added
• Documentation has been updated