chore: only push to AppHub if build was created

[jenniferarnesen]

There are 2 main improvements to the workflow to help solve all the failing builds:

• Instead of complex if statements in the gh workflow file (they aren't even working anyway!), use commit_analyzer config to prevent release for our [skip release] and [skip ci] PRs.
• publishing to AppHub fails if there is no build file, which there won't be in the case of chores and [skip release]. So add an if statement that checks for an env var. The env var gets set to true if there is a build.

Here's some workflow outputs that demonstrate the above changes in a test repo:

build_exists has been set to true and Publish AppHub runs: https://github.com/jenniferarnesen/dhis2-ci-demo/actions/runs/11667460947/job/32484827377

Skip publishing to App hub when [skip release] (even when the commit was a fix or feature): https://github.com/jenniferarnesen/dhis2-ci-demo/actions/runs/11681915720/job/32527955692#step:5:55

[dhis2-bot]

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[dhis2-bot]

🎉 This PR is included in version 100.7.5 🎉

The release is available on GitHub release

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