Add git hash to the heartbeat response

[milosmns]

Provide a brief summary of the planned work

Similarly to how we push the version in the heartbeat response, we should include the git hash. This helps with consumer trust and shows that the service published is indeed the one we build in the open.

Detailed overview

There should be an easy way to pull the Git hash from the Gradle script; with that hash value, we can push it into the generated.properties file together with the app version. The name can be something like git_sha

How the version is pulled into the project:

build.gradle.kts:128 - propertyGenerator task

Then, we should pull it further into the Configuration bean:

com.appifyhub.monolith.util.meta.BuildMetadata

And finally, we should include it in the heartbeat response:

com/appifyhub/monolith/features/heartbeat/api/model/HeartbeatResponse.kt:10

List the acceptance criteria

• The new git_sha property is available in the Heartbeat response
• Tests are updated to reflect the change
• Documentation is updated to reflect the change

Include any additional notes (optional)

No response