Custom rules for verifying defaults against enums

[hawkeyexl]

Originated from the Write the Docs slack.

[lornajane]

When reviewing, note that the code sample example is really similar to the changes I just merged in from #42 (the PRs were open at the same time)

[hawkeyexl]

Please additionally note that they are similar because the code from #42 was in part based on the code present in this PR. The rules between the PRs are similar but distinct and complimentary.

[adamaltman]

https://github.com/Redocly/redocly-cli-cookbook/pull/42/files#r1809495936
I left this comment on another similar PR. This doesn't feel so practical. Most people don't have bash samples and use curl for example (so "bash" is probably a rare/niche example for Redoc users).

I think it might be nice since this PR contains two separate plugins to separate it into two PRs, because the default enum one would be easy to approve.

This one should should probably be modified. I think the plugin would be more useful if it accepted an array of languages in the configuration and gave an error or warning (depending on severity) based on the list matching.

This is also similar to #42 , and I think if this was made more flexible should replace it. That one has a lot of quirks and hardcodes errors and warnings instead of taking the severity from the configuration.

[hawkeyexl]

@adamaltman For now, I removed the bash example rule entirely. When I get a chance, I'll see if I can whip something together that's better suited, but I don't want to block the default/enum rule from getting merged.

[hawkeyexl]

Removed require-bash-sample rule.

[adamaltman]

🎉 Thank you @hawkeyexl !