Publish JS client as NPM package

I'd like to build a UI for QuickWit, in my case in Svelte. I can either read the docs and build a JS client myself, or... Perhaps re-use the client.ts from QuickWit.

I think having an official NPM package helps to attract users and prevent issues. API changes in the REST API or query syntax might be abstracted away in a JS API. Building more complex queries might become easier using type-safe objects instead of manually building a query string.

Some thoughts on doing this:

• Splitting up the JS codebase means this will become a project with multiple packages. This means you'll want to use workspaces.
• I think the package will need to have the models.ts, client.ts and urls.ts files.
• I recommend switching from yarn to pnpm, which also supports workspaces, but is faster than yarn and provides better dev UX, in my opinion
• I recommend switching from react-app-rewired to vite. It's very fast, provides good dev UX and supports typescript out of the box.
• Currently, many types use null to indicate optional fields. This leads to very verbose API usage, as every optional field now needs to be explicitly passed in order for the typecheck to succeed. I suggest changing this to undefined by using the question mark syntax in interfaces. E.g.: indexId: string | null to indexId?: string
• The search method (and SearchResponse) should probably take a generic param so the results can be typed., signature becomes async search<ResultType>(: SearchRequest): Promise<SearchResponse<ResultType>>
• Having a builder for queries would be helpful, these can then escape special characters in keys and such.

Start with quickwit-ui/src/services/client.ts and the related models.ts and urls.ts files mentioned in the issue, then inspect how the current UI JavaScript project is organized. Done would mean an agreed, maintainable official NPM package with a defined package structure and API scope; the issue leaves the workspace, build, optional-field, generic-search, and query-builder changes open.