feat(rust): allow authenticating into multiple hosts

[imobachgs]

Problems

• CLI does not allow logging in to multiple systems #2261.
• Any connection problem is reported as an certificate problem when it is not true. To make things worse, Agama asks the user whether to accept an insecure connection (even if that's not the problem).
• Agama will perform an HTTP request even if it is not needed (e.g., agama auth show).

Solution

Storing one token per host

Instead of storing the token in $HOME/.agama/token, use a file ($HOME/.local/share/agama) containing all tokens (one per host). For instance:

{
  "192.168.122.145": "eyJ0eXAiOiJKV1QiLCJhbGciOiJIUzI1NiJ9.eyJleHAiOjE3NDUzMTg2MTV9.G36w8NQ-ZCAkCQGGwjajRpd8EfkOM8fFLLfGjzTAqP0"
}

Do not ask for insecure connections

If there is a problem when connecting to the API, just report the error (no matter whether it is an SSL problem or not). The user can use the --insecure flag to disable certificate checks.

Testing

• Added a new unit test
• Tested manually

[teclator]

LGTM

[ancorgs]

I can confirm the conflict was properly resolved. I didn't check the rest, but I will rely on previous @teclator approval to say that this LGTM.

[mvidner]

When there is any problem with the file storing the authentication tokens, do we tell the user where it is (agama auth login --help?) or do they have to resort to strace?

Also, my testing use cases involve multiple agamas on the same host but different ports. I hope it continues to work :)

[mvidner]

Neat!