fix: solution merges stuck at 'Awaiting PR Merge'

[ewingjm]

Purpose

Solution merges outside of the environments used for testing the Development Hub will be stuck on 'Awaiting PR Merge' if using a pull request source control strategy.

Approach

Updates flow template to remove hard-coded organisation, project, and repository and replace it with variable tokens to be substituted.

TODOs

• [x] Automated test coverage for new code
• [x] Documentation updated (if required)
• [x] Build and tests successful