telemetry: add metrics for iam credentials authentication (#1070)

## Metrics Modified:
`auth_addConnection`: add `credentialType` type to record distinguish
IAM and other login method.


## License

By submitting this pull request, I confirm that my contribution is made
under the terms of the Apache 2.0 license.

---------

Co-authored-by: Ramon Li <liramon@amazon.com>

Author: yuxianrz

telemetry/definitions/commonDefinitions.json

@@ -3924,6 +3924,10 @@
                     "type": "credentialStartUrl",
                     "required": false
                 },
+                {
+                    "type": "credentialType",
+                    "required": false
+                },
                 {
                     "type": "featureId"
                 },