Extract init-script contents out of 'develocity-gradle.yml'

[bigdaz]

Previously, init-script content was inlined directly into 'develocity-gradle.yml'

To facilitate sharing and ease maintenance, these contents have been extracted into separate files.

• Raw init-script content in src/gradle/init-scripts
• Template for yml file in `src/gradle/develocity-gradle.template.yml'
• Build script to regenerate final yml is build.sh
• New GitHub Actions workflow will regenerate the develocity-gradle.yml output and push changes, if any.