Migrate build to GitHub actions

[mhalbritter]

• Migrate build to GHA
• Migrate to Azure Spring Apps
• Add Google Chat notifications

[mhalbritter]

After we added the initialzr.stats.elastic.uri placeholder, those warnings appeared in the tests:

2024-02-05T12:02:21.705+01:00  WARN 160821 --- [   initializr-8] i.s.i.a.s.ProjectGenerationStatPublisher : Failed to publish stat to index, document follows 

{"generationTimestamp":1707130479523,"type":"maven-project","buildSystem":"maven","groupId":"com.example","artifactId":"demo","javaVersion":"17","language":"java","packaging":"jar","packageName":"com.example.demo","version":{"id":"3.1.0","major":"3","minor":"3.1"},"dependencies":{"id":"cloud-starter-vault-config testcontainers","values":["testcontainers","cloud-starter-vault-config"],"count":2}}

We need to find a way to either disable the elastic stuff when the property is set but is empty, or only include the property when the application is deployed (e.g. through a profile).

[mhalbritter]

I have paused the Concourse pipeline.