Allow annotating code with external linter on demand or add debounce option

[panstromek]

I really like the clippy & cargo check integration, but I'd like to run it only on demand (with a shortcut) or debounce it a lot more than what it is now. ATM I can run linter on demand, but it only opens inspection window, it doesn't annotate code.

There are two main reasons:

1. I use wasm-pack with webpack-dev-server, which watches files and rebuilds automatically after every change. When on-the-fly annotation is enabled, IntelliJ need to autosave way more often, which triggers both linter and Webpack build - this slows down IDE a lot, moreover sometimes these two fight for file locks, blocking each other (as pointed out in Intellij-rust should stop external linter before running #4283). I think that especially in this use case, it'd be better to annotate only on-demand. I see no other simple way around that.

2. IntelliJ runs the linter way more often than necessary, often during typing, which means that recieved annotation is invalidated almost immediately. Seems like it's throttled, not debounced. I'd prefer it to be running only when It's clear that I stopped typing. Running it also slows down IDE noticeably, so it better be worth it. As an example, I think ESLint integration is better tuned in this sense.

Thanks and have a great holidays ;)