Add OpenSearch support

[foster-hangdaan]

This is a UX improvement which adds the ability to search JSR packages without having to navigate to jsr.io first. On Firefox, a plus icon appears on the search bar which allows the user to add jsr.io as another search engine.

npmjs.com supports this feature:

jsr.io does not:

References:

• OpenSearch Documentation
• MDN: OpenSearch description format
• The Chromium Project: Tab to Search

[yossydev]

Can I take up this issue?

[lucacasonato]

@yossydev Yes, absolutely!