Support Credentials from IAM Roles Anywhere

**Is your feature request related to a problem? Please describe.**
When I using credentials from IAM Roles Anywhere, I'm unable to use Cloudwatch Agent, since in OnPrem mode it looks for hard-coded Access Keys in the .aws config files

**Describe the solution you'd like**
I'd like to use the standard IAM Roles Anywhere service, or the credential_process.

**Additional context**
I've persued the "RUN_WITH_IRSA" config mode, but this is very poorly documented and also doesn't seem to solve the issue.

Start by tracing the OnPrem credential-loading path that reads the .aws configuration files, then review the RUN_WITH_IRSA configuration and its documentation. Check how credential_process and IAM Roles Anywhere credentials are expected to be selected; done means the CloudWatch Agent can obtain credentials through the requested standard mechanism without hard-coded access keys.

Written by the indexing model from the issue text.