Conf macro improvements part 2

[camsteffen]

changelog: none

Follow-up to #7150

I made the default value required again for define_Conf! so that it can be parsed by the magic Python. I guess it's just as well for readability.

r? @flip1995

[flip1995]

One documentation update missing: https://github.com/rust-lang/rust-clippy/blob/master/doc/adding_lints.md#adding-configuration-to-a-lint

[flip1995]

@bors r+

Thanks!

[bors]

📌 Commit ffb0951 has been approved by flip1995

[bors]

⌛ Testing commit ffb0951 with merge f41f380...

[bors]

☀️ Test successful - checks-action_dev_test, checks-action_remark_test, checks-action_test
Approved by: flip1995
Pushing f41f380 to master...

[flip1995]

Lol, this backwards broke the beta deploy: 7c7683c

Remind me in 6 weeks, that this will also break the stable 1.53 release deploy 😄

(Not your fault of course)

[camsteffen]

What happened?

[flip1995]

The deploy workflow checks out the scripts from the current master branch, so we don't deploy an old state of the website for beta and releases. Otherwise it would use the deploy and website generation scripts that were in the repo at the point of the release (6/12 weeks ago). Especially when I first implemented the deploy workflow this lead to many failures of beta/stable deployment. Maybe we could use the python scripts in util for releases and just checkout the .github/deploy.sh from master. But since the effects of this will only show in 6/12/42069 weeks, I'd rather not change this usually-working workflow. I will just hand update the gh-pages for the next 2 releases and we should be fine. Especially, because #7172 will take over the job of generating the deploy artifacts anyway in the future.