feat(rust): add syntax highlighting to shell script examples

[jlucktay]

Current Behavior

Shell script examples in help messages are plain text and not styled at all.
Ref: #3311

Proposed Changes

Makes use of the syntect crate to run a syntax highlighting pass over the example shell scripts for the ockam command.

Setting this PR as a draft for this first pass as it only affects the base command and not any sub-commands yet, to see whether or not the implementation is a good fit for this project.

Details

I split const HELP_TEMPLATE: &str in half to make things a bit simpler in the newly-added highlight module and its shell_scripts function. Let me know if this looks OK and I can apply the same pattern across the other sub-commands.

Colour samples

These are the different themes available in the crate.
Each has the bg: bool flag toggled on and off for background highlighting.
Click for bigger images.

InspiredGitHub:

Solarized (dark):

Solarized (light):

base16-eighties.dark:

base16-mocha.dark:

base16-ocean.dark:

base16-ocean.light:

Let me know which theme suits best.
For my 2p it's base16-mocha.dark with bg false.

Checks

• All commits in this Pull Request are signed and Verified by Github.
• All commits in this Pull Request follow the Ockam commit message convention.
• I accept the Ockam Community Code of Conduct.
• I have accepted the Ockam Contributor License Agreement by adding my Git/Github details in a row at the end of the CONTRIBUTORS.csv file in a separate pull request to the build-trust/ockam-contributors repository.

[mrinalwadhwa]

@jlucktay this looks fantastic! congratulations on your first PR.
I think base16-mocha.dark with bg false looks quite good.

I tried various preset themes in iTerm to see how it would render for people and I think people with light backgrounds won't have a great experience. So I'm wondering if we can do something to improve that 🤔

[mrinalwadhwa]

I tried various preset themes in iTerm to see how it would render for people and I think people with light backgrounds won't have a great experience. So I'm wondering if we can do something to improve that 🤔

Wonder what other projects that render code on the terminal handle this.
Delta comes to mind as an example https://github.com/dandavison/delta

[mrinalwadhwa]

@jlucktay this is already very useful for some of the help improvements that I am working on today. So I hope you won't mind if I land right now. If you think of any further improvement, follow on PRs are very welcome!

Congratulation on an awesome first contribution 🥂

[mrinalwadhwa]

Found a really nice article on adjusting color. Thank you @Canop 🙏
https://dystroy.org/blog/terminal-light/

[Canop]

Found a really nice article on adjusting color. Thank you @Canop pray https://dystroy.org/blog/terminal-light/

You're welcome. I'd be interested to see how you used it.