Integrations: generic API incoming webhook uses APIv2

[humitos]

When creating a "Generic API incoming webhook" it gives you a link and a token to be able to make a request and trigger a build for the project. The URL uses APIv2 which is deprecated and should not be used anymore.

Now, we have APIv3 that allows triggering builds without creating an incoming webhook. See https://docs.readthedocs.io/en/stable/api/v3.html#build-triggering

There is one noticeable difference between these two:

• APIv2 uses a token that's valid only for that particular endpoint
• APIv3 requires a user token