Add the ability to customize token header

[travishathaway]

What is the idea?

Token headers can come in different shapes and forms. Currently, we support the following formats:

Authorization: token <token>

and

Authorization: Bearer <token>

Instead of adding more and more types, let's just make the token header configurable.

Why is this needed?

To be flexible enough to support any header token setup.

What should happen?

The conda auth login --token command should receive a new --header/-h option that will allow for customizing the name of the token header. It should also accept a --token-template option that will accommodate adding extra text to the header field.

The following will be possible afterwards...

Setting a custom header name:

conda auth login --token --header X-Auth

Setting a custom header name and a template for the token value:

conda auth login --token --header Authorization --header-template 'Bearer {token}'

Additional Context

No response