Add the Datadog AI Proxy provider

[jamesponddotco]

What does this PR do?

Add support for the Datadog AI Proxy provider, which is a provider that can be used by Datadog employees.

Additional Notes

Need to add internal documentation in Confluence about the DOCUMENTOR_ENDPOINT variable, with the correct value to use, as the endpoint shouldn't be shared publicly.

Also, the linting workflow will fail, but a PR with a fix exists at the link below:
#6

Review checklist

Please check relevant items below:

• The title & description contain a short meaningful summary of work completed.
• Tests have been updated/created and are passing locally.
• I've reviewed the CONTRIBUTING.md file.