feat($plugin-search): Add support for search hotkeys

[evaera]

Summary

Adds hotkey to focus SearchBox component with configurable keys, defaulting to s and /.

This makes it much easier to switch to the docs and focus the searchbox when using documentation in tandem with programming. Sites like docs.rs and even GitHub itself support this behavior.

Fixes #624

What kind of change does this PR introduce? (check at least one)

• Bugfix
• Feature
• Code style update
• Refactor
• Docs
• Build-related changes
• Other, please describe:

Does this PR introduce a breaking change? (check one)

• Yes
• No

The PR fulfills these requirements:

• When resolving a specific issue, it's referenced in the PR's title (e.g. fix #xxx[,#xxx], where "xxx" is the issue number)

You have tested in the following browsers: (Providing a detailed version will be better.)

• Chrome
• Firefox
• Safari
• Edge
• IE

If adding a new feature, the PR's description includes:

• A convincing reason for adding this feature
• Related documents have been updated
• Related tests have been updated

[kefranabg]

Nice job @evaera 💪

[flozero]

Hello thank's for your work ! Can please add the event on function and destroy the event on the lifecycle beforeDestroy please

[evaera]

@f3ltron Yes, it's been updated.

[vue-bot]

Hey @evaera, thank you for your time and effort spent on this PR, contributions like yours help make Vue better for everyone. Cheers! 💚