Fix SSM endpoint for Gov regions

[shreyamalpani]

What does this PR do?

Overrides the SSM url to be ssm-fips.{REGION}.amazonaws.com only in commercial FIPS mode. Gov endpoints should use the default ssm.{REGION}.amazonaws.com. https://docs.aws.amazon.com/general/latest/gr/ssm.html

Motivation

Customer reported Datadog Forwarder getting API key from SSM in gov region is not working SLES-2580

Testing Guidelines

Additional Notes

Types of Changes

• Bug fix
• New feature
• Breaking change
• Misc (docs, refactoring, dependency upgrade, etc.)

Check all that apply

• This PR's description is comprehensive
• This PR contains breaking changes that are documented in the description
• This PR introduces new APIs or parameters that are documented and unlikely to change in the foreseeable future
• This PR impacts documentation, and it has been updated (or a ticket has been logged)
• This PR's changes are covered by the automated tests
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[joeyzhao2018]

1. Based on aws doc, not all commercial regions support ssm-fips endpoint.
2. When the configuration explicitly enabled FIPS mode but the endpoint is not supported, a warning log is needed IMHO.

[joeyzhao2018]

LGTM