Add support for RUNNER_NAME

[jkupferer]

Description

Add support to set the GitHub runner name by use of RUNNER_NAME environment variable while maintaining default to hostname.

Related Issue(s)

#35

Checklist

• [x ] This PR includes a documentation change
• [ ] This PR does not need a documentation change

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• [ ] This PR includes test changes
• [ x] This PR's changes are already tested

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• [ ] This change is not user-facing
• [ ] This change is a patch change
• [ x] This change is a minor change
• [ ] This change is a major (breaking) change

Changes made

Update register.sh to default the runner name to environment variable RUNNER_NAME with default to hostname.