provide flag value autocomplete for --param

[heyjcollins]

Description of problem

app devs appreciate efficiency and convenience.
providing broad support for autocompleting flag values makes it possible for people to NOT remember names of items added previously by them or others.

providing autocomplete for flag values inconsistently is a bad UX and we should do all that we can to consistently deliver on the contract.

Proposed solution

apps plugin already supports autocomplete for some flag values (e.g. --namespace --- will return list of possible namespaces)

Add similar support for --param

When I've typed --param then press <TAB>, all the current param keys associated with my workload, and any params associated with any of the supply chains on the target cluster, are auto-suggested.
When --param flag/value has already been specified, autocomplete should only suggest params which haven't already been specified in the command.