Add support for specifying port of custom endpoint in IamAwsProvider

[jgolda]

Currently IamAwsProvider accepts providing a custom endpoint of IMDS service. It's great for testing, but in my opinion could be further improved by allowing the class'es client to provide a custom port as well. Currently in order to setup a local testing environment the user needs to set up a mock endpoint listening on port 80, which is sometimes not acceptable (eg. collides with other services).

Let me know if you're interested in such a feature. If so, i'll prepare a PR

[balamurugana]

You could use customEndpoint argument to the constructor of IamAwsProvider class.

[jgolda]

Not really, as the url provided via customEndpoint is later parsed and the port part is ignored, only scheme, hostname is used, eg in io.minio.credentials.IamAwsProvider#fetchImdsToken.
If the user passes eg. http://localhost:8180 then minio client attempts to connect to http://localhost:80 (as 80 is default). There is no way around it

[balamurugana]

Feel free to send a fix WRT customEndpoint usage