Add Python examples for API v3 documentation

[humitos]

We already have cURL request examples for APIv3 docs at https://docs.readthedocs.io/en/latest/api/v3.html#get--api-v3-projects-

It would be awesome to have use sphinx-tabs to have multiple tabs. One with the cURL example we already have there and another Python tab with the same request using Python code with Slumber

If Slumber is not good enough for this, we can use just requests as the example from here https://docs.readthedocs.io/en/latest/guides/environment-variables.html

Ref: #5895 (comment)

[tapaswenipathak]

Hi @humitos: Is the ticket open? Can I add a PR?

[humitos]

@tapaswenipathak yes, sure!

[dibyaaaaax]

hey @humitos, can I work on this?

[humitos]

@dibyaaaaax sure! go ahead :)

[humitos]

This is already done in the linked and merged PR.