Re add toplevel py.typed file

[jenshnielsen]

Description

This will ensure that the top-level opentelemetry module is marked as typed.
This was removed as part of #3385
where py.typed files were correctly added to submodules. However, a file at the top level is also required

In 1.26.0 if you try to to run pyright against a simple line such as:

from opentelemetry import trace
This will fail with an error such as

 pathtosomefile.py:12:6 - error: Stub file not found for "opentelemetry" (reportMissingTypeStubs)

An example of this failing can be seen in microsoft/Qcodes#6279

Type of change

• Bug fix (non-breaking change which fixes an issue)

How Has This Been Tested?

Manually ran pyright against code that fails with 1.26.0 against main branch with this fix and confirmed that error is gone

Does This PR Require a Contrib Repo Change?

• No.

Checklist:

• Followed the style guidelines of this project
• Changelogs have been updated
• Unit tests have been added (N/A)
• Documentation has been updated (N/A)