feat: composition

[e-krebs]

Summary

This PR currently adds two things:

• new compositionID optional parameter when initializing InstantSearch
  • instantsearch({ compositionID: 'composition-2', searchClient });
• new searchWithComposition method in AlgoliaSearchHelper to handle querying the composition API
• also, since we have to use a root index component (automagically added) under the hood, I had to adapt the AlgoliaSearchHelper signature to handle being initialized with an indexName vs. a compositionID
  • I made it so this is backward compatible
  • maybe there's a better way?
  • we're using the index parameter internally to store the compositionID. The main reason for that is: this is the simplest way to be out of the box compatible with the sortBy widget

Result

I'm currently modifying the js > getting-started example. A dedicated example will be added later.

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Sandbox	Source
example-instantsearch-getting-started	Configuration
example-react-instantsearch-getting-started	Configuration
example-react-instantsearch-next-app-dir-example	Configuration
example-react-instantsearch-next-routing-example	Configuration
example-vue-instantsearch-getting-started	Configuration

[e-krebs]

@Haroenv as discussed, this should be ready to merge but we won't merge for now (and instead use this as a base branch for the whole feature implementation) so I'm keeping the "do not merge" label