Description

When the key is missing while accessing a route with the key-auth plugin enabled, we get the message, "Missing API key found in request," which isn't correct. How is something missing in the request, found in the request?

Instead, it should be phrased as "Missing API key in request," which is clearer.

While users may be able to make sense of the older message, it is an easy enough change.

This PR updates the message in the code, tests, and docs.

Checklist

• I have explained the need for this PR and the problem it solves
• I have explained the changes or the new features added to this PR
• I have added tests corresponding to this change
• I have updated the documentation to reflect this change
• I have verified that this change is backward compatible (If not, please discuss on the APISIX mailing list first)