Support "multi-choice" input type for manual workflows

Describe the enhancement
Current set of input types doesn't cover some use-cases for manual workflows

We use a single gh-action as an entrypoint of deploying packages from our monorepo, and sometimes we need to manually deploy several packages simultaneously. Up until now we just went with a set of Booleans, so we could tick all the packages we needed to run our CI/CD against via UI. However, we speedily reached a limit of 10 input values

Introducing an input type that would store a, say, json array could help:

on:
  workflow_dispatch:
    inputs:
      name:
        type: multi-choice
        description: select packages
        options: 
        - go-service1
        - go-service2
        - py-service1

...and in fact would be more logical with less copy-paste overhead for our use-case

The issue centers on workflow_dispatch inputs in GitHub Actions; start by tracing how the runner handles manual workflow inputs and review the discussion for established semantics. Done means a supported multi-choice input with a defined representation, such as the proposed JSON array, and documented behavior, but the issue does not identify files or tests.