Add stdin option to command chains

[maksimowiczm]

Description

Describe the change. If there is an associated issue, please include the issue link (e.g. "Closes #xxx"). For UI changes, please also include screenshots.

Added stdin field on the !command variant. Stdin is now piped into command using ChildStdin. It is still compatible with previous command variant.

Closes #190

Known Risks

What issues could potentially go wrong with this change? Is it a breaking change? What have you done to mitigate any potential risks?

Calling command may be unsafe, but I don't think it carries any new threat.

QA

How did you test this?

Added one unit test. Probably need to add more.

Checklist

• Have you read CONTRIBUTING.md already?
• Did you update CHANGELOG.md?
  • Only user-facing changes belong in the changelog. Internal changes such as refactors should only be included if they'll impact users, e.g. via performance improvement.
• Did you remove all TODOs?
  • If there are unresolved issues, please open a follow-on issue and link to it in a comment so future work can be tracked

[maksimowiczm]

There is still some work to do (docs and tests). I wanted to see what are your thought on this.

[LucasPickering]

Looks good, I tested this locally and it's working great. Just left some feedback on minor tweaks. In addition to adding the field in chain_source.md, could you do a search for /sh.*-c/ in the docs (I found two results) and change those examples to use this new field? Thanks!

[maksimowiczm]

Sorry, had to do some force pushes because my editor reformatted md files 😅

[maksimowiczm]

I have no idea for any new tests. I think it is ready to merge.

[maksimowiczm]

Resolved conversations. Not sure about the test name.

[LucasPickering]

Looks good, you have conflicts though so I can't merge it. Could you rebase onto master please?

[LucasPickering]

Looks good, you have conflicts though so I can't merge it. Could you rebase onto master please?

Never mind, I forgot I can also make edits. The conflicts where just on the changelog so I resolved and squashed.