Await writing template to temp directory

[TimCsaky]

Attempt to handle a race condition during copying template from temp directory to the file cache

Description

Ticket: https://apps.nrs.gov.bc.ca/int/jira/browse/SHOWCASE-3693

• await the completion of writing template to temp directory before progressing to move the file.
• simplified code to define a temp file name
• added some minor code comments

Types of changes

Bug fix (non-breaking change which fixes an issue)

Checklist

• [x I have read the CONTRIBUTING doc
• I have checked that unit tests pass locally with my changes
• I have added tests that prove my fix is effective or that my feature works
• I have updated the OpenAPI 3.0 v*.api-spec.yaml documentation (if appropriate)
• I have added necessary documentation (if appropriate)

Further comments

[github-actions]

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