Support Camunda 8 secret syntax in FEEL expression

[barmac]

Problem you would like to solve

Secrets syntax is not detected in the Modeler:

I am forced to switch tabs and google for it (or search for an example where I used it)

In case I make a mistake, I find out about it in runtime only.

Proposed solution

Extend the FEEL syntax with Camunda 8 secrets syntax. Possibly provide suggestions. In Web Modeler, specific secret names could even be provided.

Alternatives considered

Leave it as is.

Additional context

Reported by @berndruecker via https://camunda.slack.com/archives/C0693F1NFK5/p1728541633050579

[nikku]

Challenge to overcome here: Secrets are only supported in some places, i.e. only in connectors or potentially other workers that support them. We could decide to always recognize the pattern and ignore this matter.

However, I think the real user problem to solve here is that you cannot easily use secrets, and that "known secrets" are not suggested? There, as mentioned, this is much better tackled via auto completion and/or some sort of inline help, cf. bpmn-io/bpmn-js-properties-panel#708, or this mock-up:

I propose to rewrite the issue to capture the user problem more broadly. This allows us to consider the right set of changes for "enabling users to better work with secrets in Camunda".