Addd support to forward environment variables fo ProcessCredentialsProvider, so context like proxy config can be passed to the process.

closes #5688

Motivation and Context

using aws_signing_helper in a locked down environment need proxy settings. Needing to support global proxy environment variables tend to be confusing

Modifications

added env method in builder that can be used to inject environment variables.
forwarded these variables so they are available when the process runs
changed the process scripts so they can also accept variables from environment

Testing

updated the tests, so they test the happy case when there are variables defined

Screenshots (if appropriate)

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)

Checklist

• I have read the CONTRIBUTING document
• Local run of mvn install succeeds
• My code follows the code style of this project
• My change requires a change to the Javadoc documentation
• I have updated the Javadoc documentation accordingly
• I have added tests to cover my changes
• All new and existing tests passed
• I have added a changelog entry. Adding a new entry must be accomplished by running the scripts/new-change script and following the instructions. Commit the new file created by the script in .changes/next-release with your changes.
• My change is to implement 1.11 parity feature and I have updated LaunchChangelog

License

• I confirm that this pull request can be released under the Apache 2 license