Improvements to command querying

[LucasPickering]

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.

• Kill pending query process when a new one is started
• Add a keybind (?, same as help dialog) to view the error when a command fails
  • We report a notification when this happens that includes the keybind
• Add commands.shell config field, to define how all commands should be executed
  • Defaults to sh -c, so you can now use pipes in the query out of the box
• Add commands.default_query to define an initial query string for all responses. For example, default_query: jq will pre-populate the box with jq so you can start writing actual queries faster

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?

• Help dialog
• Default/persistence interaction
• I haven't tested this on Windows at all

QA

How did you test this?

Added a good amount of unit tests

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