Support reading input from stdin or based on value in an Apalache `.cfg` source

[shonfeder]

With #2127 and #2074 in place, it will now be quite easy to adjust the CLI to support more flexible input methods:

• [ ] 1. Read specification input from stdin.
• [ ] 2. Read specification input based on a file or string give in a configuration source.

For 1, the CLI invocation might look like:

json-data-cmd | apalache-mc check --stdin=json

For 2, the CLI invocation can simply be

apalache-mc check --config=myconfig.cfg

In both cases, we'd do error handling prior to running the pass executor to report a user error in case no input source was provided.