Change DataSourceHealthIndicator details from "hello" to "result"

[philwebb]

See this comment. Let's do that as a separate issue to we can track it.

[restolho]

@philwebb This would be my first contribution to an open source project but it seems simple enough (change the String from hello to result + tests, correct?). You think i could take this?

[philwebb]

@restolho Yes please, that would be great! If you need any help just shout.

[snicoll]

Closing in favour of PR #15136