{Extension} insert extension directory in head of sys.path

[fengzhou-msft]

Description of PR (Mandatory)
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Fix #12062.
The extension directory was appended to the sys.path, and the virtual env site-package directory was in front of it. So CLI will load the SDK installed in the virtual env instead of the one in extension directory. Now we put extension directory in front position of sys.path to be loaded priorly.

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[yonzhan]

add to S167

[yungezz]

hi @fengzhou-msft when user is using venv, it's by design all packages should be loaded from venv, right? Will sync with you offline on this.

[arrownj]

LGTM

[jiasli]

I debugged into

azure-cli/src/azure-cli-core/azure/cli/core/__init__.py

Line 231 in 34f9033

sys.path.append(ext_dir)

ext_dir is like 'C:\\Users\\xxx\\.azure\\cliextensions\\support'.

In that case, if two extensions contain the same SDK but with different versions, it will still has conflict.

Another concern is that allowing extensions to override SDKs from venv may cause a security breach - a malicious extension can inject tampered SDKs to intercept the calls thus overriding the behavior, also impacting other command modules that rely on the SDKs.

So as an ultimate solution, the extension should vendor the SDK by putting it under vendored_sdks to avoid the conflict. Then they can use something like from .vendored_sdks.timeseriesinsights.models import LongTermEnvironmentUpdateParameters.

[jiasli]

Better to sync with the issue creator to vendor the SDKs instead.