opentelemetry-api: avoid SelectableGroups dict API

[Mirochill]

Description

Fixes #5231.

Normalize importlib.metadata SelectableGroups through select() instead of the deprecated dict-style interface. This preserves the existing cached all-entry-points behavior while avoiding the Python 3.10/3.11 SelectableGroups dict interface is deprecated warning path.

Type of change

• 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?

• git diff --check
• git diff --cached --check

Local tests, tox, linters, builds, installers, and project scripts were not run, per this workspace policy; remote GitHub CI will be used. A regression test is included for the SelectableGroups.select() normalization path.

Does This PR Require a Contrib Repo Change?

• Yes. - Link to PR:
• No.

Checklist:

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

The PR is draft until the first remote checks are available.

[linux-foundation-easycla]

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