fix: add netrc auth for sources

[AndreyNautilus]

I implemented the approach we discussed in the chat, but now I start to think that this is maybe not the correct interface. I don't think users should explicitly specify that they want to use netrc file for authentication for http sources:

authentication:
  type: "basic_netrc"

Netrc file is more a system level configuration rather than application level, so users should not explicitly declare it. If netrc file is configured it should just work. We can try to fetch credentials from netrc file for every download request in HttpPackageSpec - that shouldn't affect the performance too much. On the other size, for other auth methods, like "basic auth" users indeed should explicitly provide required data:

authentication:
  type: "basic"
  login: "ENV: <env variable name>"
  password: "ENV: <env variable name>"

So, I suggest to drop "basic_netrc" configuration and assume it's always enabled.

I'll add tests when we agree with the approach.

[RobvanderMost-TomTom]

Yes, I think it makes sense to support netrc as default without configuration. And when the authentication type is explicitly overrideen we would then not read from netrc.

[RobvanderMost-TomTom]

Could you please target branch develop-0.8.x? Then I can make a proper 0.8.x release afterwards.