feat: add azure functions integration

[duncanpharvey]

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• PR author has checked that all the criteria below are met
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• The change includes tests OR the PR description describes a testing strategy
• The PR description notes risks associated with the change, if any
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Reviewer Checklist

• Reviewer has checked that all the criteria below are met
• Title is accurate
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• Testing strategy adequately addresses listed risks
• Newly-added code is easy to change
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• If necessary, author has acknowledged and discussed the performance implications of this PR as reported in the benchmarks PR comment
• Backport labels are set in a manner that is consistent with the release branch maintenance policy

[github-actions]

CODEOWNERS have been resolved as:

ddtrace/contrib/azure_functions/__init__.py                             @DataDog/apm-core-python @DataDog/apm-idm-python
ddtrace/contrib/azure_functions/patch.py                                @DataDog/apm-core-python @DataDog/apm-idm-python
ddtrace/contrib/internal/azure_functions/patch.py                       @DataDog/apm-core-python @DataDog/apm-idm-python
ddtrace/_monkey.py                                                      @DataDog/apm-core-python
ddtrace/ext/__init__.py                                                 @DataDog/apm-core-python @DataDog/apm-idm-python