fix(auth): use api_key instead of auth_token

[litury]

Countly API expects api_key parameter, not auth_token.

Fixes authentication errors (400 Bad Request) when using MCP tools.

[ar2rsawseen]

Hello
initial version actually used api key, but it did not pass internal security checks.
Providing API key which is global and irrevocable to AI was a big red flag, so we had to change it to auth_tokens, which can be time limited, use limited and even scope limited (working for specific endpoints)
Since tokens are available on both Lite and Enterprise versions, we thought it would be fine to use only those.
So it is mostly from security perspective

Did you have any problems using auth tokens?