fix: skip key validation if endpoint is different

[JamieDanielson]

Which problem is this PR solving?

• Closes Agent vails validation and cannot start if an alternative API endpoint is used #264

Short description of the changes

• Check endpoint and if it differs from our default, skip the api key validation
• Move the Config Validate below the logging of config values; that way, if there is something wrong, the config values are printed out first for easier troubleshooting if it fails.

I'd considered some refactoring to pull out defaults and use a variable instead of hardcoding here, but wasn't sure it was worth the extra cleanup for this rare use case.

How to verify that this has the expected result

Set an incorrect API Key. With no change to endpoint, or endpoint set to "https://api.honeycomb.io", agent pod should fail to start because of invalid key - and should log the config options followed by the fatal error. With a different endpoint, agent should start with no failure.