[eng] auto PR created with PR of http-client-python

[msyyc]

Now autorest.python depends on http-client-python. Once there is PR A for http-client-python, we hope there is another PR B in autorest.python repo which depends on A. To promote the development efficiency, it is nice if the PR B is auto generated by bot or pipeline.

[iscai-msft]

This is a good issue, @hallipr would you be free for me to go over this with you and help?

[msyyc]

Before PR B could be generated automatically, we shall manually create it once open PR A. Here is guidance:

1. Create PR A in microsoft/typespec （e.g. here）
2. After CI of PR A passes, get the url of private package in CI (e.g. here)
   
3. Create PR B with the url (e.g. here)
4. Make sure CI of PR B pass.
5. Only when CI of PR B pass, we can merge PR A.