Add ability to auto complete fields

[nikku]

Is your feature request related to a problem? Please describe

As a user I'd love to get auto completion where available (i.e. for known called activities. I want auto completion in any place it makes sense (forms, users, groups, ...).

As a tool integrator I want to decide where to get that information from and provide it accordingly.

Describe the solution you'd like

• Offer a generic extension point for auto completion in the properties panel

Describe alternatives you've considered

Implement auto completion on a case by case basis

Additional context

An example how auto completion could look like for call activities:

Another example how this can provide dynamic hinting (i.e. on configuration of secrets in C8 SaaS):

---

Supports https://github.com/camunda/team-connectors/issues/80, https://github.com/camunda/product-hub/issues/1003