Add CLI support for input list expansion

[AevaOnline]

Describe the bug
The omnibor CLI requires multiple input artifacts be enumerated each with their own -i option, and either crashes or errors when lists are provided on the command line.

To Reproduce
Example of currently working behavior:

aeva@EOS:~/src/omnibor-rs$ omnibor manifest create -t /home/aeva/.cargo/bin/omnibor -o /home/aeva/.adg/ -i omnibor-cli/src/cli.rs -i omnibor-cli/src/app.rs
 INFO wrote manifest 'gitoid:blob:sha256:d39cfe016d22607a7538ffb588d5ef9504cc9d354233fd898c7acca24f581a71' to '/home/aeva/.adg/gitoid_blob_sha256_b88105828ad6a42e7cb3b1813871883a7d90cce256e4d04ab37d7c9a413e985d.manifest'

Example of error when providing shell expansion list input:

aeva@EOS:~/src/omnibor-rs$ omnibor manifest create -t /home/aeva/.cargo/bin/omnibor -o /home/aeva/.adg/ -i omnibor-cli/src/{cli.rs,app.rs}
error: unexpected argument 'omnibor-cli/src/app.rs' found

Usage: omnibor manifest create [OPTIONS] --target <TARGET>

For more information, try '--help'.

Expected behavior
The manifest create command should allow for a list to be passed in via normal shell manipulation means.

This does not necessarily require CSV or other formats (I tested that above just for demonstration). It should be able to, for example, take a list of arguments after a common delimiter, such as -- or after the -i option if it is the last option on the command-line.

E.g.,

$ omnibor manifest create -t $TARGET -o $OUTPUT -i $(cat $INPUT-FILE-LIST)

[alilleybrinker]

Thanks for filing this @AevaOnline! I actually think I could make the -i argument positional instead of a flag. I'd initially made it a flag to be maximally conservative, as positional arguments are less easy to update in a backwards-compatible way; but for this specific command that list of inputs will always be the primary argument, so I think positional makes sense.

[AevaOnline]

If backwards compatibility is important here, I think the equivalent outcome could be achieved by adding an optional -- separator, so that it can take either -i $VALUE repeatedly or -- $(cat VALUE_LIST)

[alilleybrinker]

The CLI itself is still pre-1.0, so I feel comfortable making a breaking change in the name of an easier-to-use API. I think the positional argument form is the one people are more likely to expect, rather than the post--- form.

[alilleybrinker]

Alright, it's merged. For now, the way to get the latest would be to install from source with cargo install -p omnibor-cli from the root of the repository. I'm debating whether it makes sense to cut a new release for this (it's the only change to the CLI since 0.8.0), but if you'd like a new release to be built let me know.

[AevaOnline]

No release needed just for this / for me, I'm fine building from source :)

thanks!