Config validator allows empty username in basic_auth

[BitProcessor]

Tested on grafana-agent 0.25.1

The following does not throw a config validation error:

          basic_auth:
            username: 
            password: SeCreT

The above is the case for metrics, logs and traces endpoints.

Result:

• if a configuration mistake is made and the username is left empty, the agent starts without issue.
• affected endpoints throw a lot of 401's

It appears that a username is required in the basic_auth spec. See: https://grafana.slack.com/archives/C01050C3D8F/p1657200458609489?thread_ts=1657199629.325379&cid=C01050C3D8F

[rfratto]

Isn't it true, generally, that the HTTP spec doesn't require usernames for Basic authentication?

I agree that you always need a username for Grafana Cloud, but I'm unsure if that's universally true for anything supporting basic auth.

[github-actions[bot]]

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