feat: enable mtls on external application application load balancer

[Tazminia]

This PR provides the following:

• Enable mTLS support on an external application load balancer by specifying a server tls policy.
• Add .python-version to git ignore for contributors with multiple python versions on their machines.

This is my first attempt contributing to the project, please let me know if I need to do further checks or changes. Also, I had tests failing but none of them seemed related to what I am changing.

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Checklist

I applicable, I acknowledge that I have:

• Read the contributing guide
• Ran terraform fmt on all modified files
• Regenerated the relevant README.md files using tools/tfdoc.py
• Made sure all relevant tests pass

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[juliocc]

I think the new flag should go under var.https_proxy_config. @ludoo wdyt?

[juliocc]

@Tazminia instead of a top level variable, can you add a field to var.https_proxy_config?

Thanks!

[Tazminia]

@juliocc of course. I will handle it and push again.

[Tazminia]

I moved the variable as requested.