Support .netrc file

[bachp]

Curl defines a .netrc format that allows to specify credentials per URL.

It is supported by various other projects including

• Git (via curl)
• Python requests

There are already ways to do this via 3rd party crates like reqwest-netrc, but it requires the reqwest client to be wrapped in reqwest-middleware. Having this feature directly in reqwests would simplify providing authentication for projects depending on reqwests. For example to provide authentication to vargo-vet.

I think it would be beneficial to be enabled by default and have a builder option to opt out no_netrc. But an opt in via with_netrc would also be work