250: Changes related to the next MeiliSearch release (v0.21.0) r=alallema a=meili-bot

Related to this issue: meilisearch/integration-guides#117

This PR:
- gathers the changes related to the next MeiliSearch release (v0.21.0) so that this package is ready when the official release is out.
- should pass the tests against the [latest pre-release of MeiliSearch](https://github.com/meilisearch/MeiliSearch/releases). Until there is an RC version, the tests should be valid against the [alpha versions of transplant](https://github.com/meilisearch/transplant/releases).
- might eventually contain test failures until the MeiliSearch v0.21.0 is out.

⚠️ This PR should NOT be merged until the next release of MeiliSearch (v0.21.0) is out.

_This PR is auto-generated for the [pre-release week](https://github.com/meilisearch/integration-guides/blob/master/guides/pre-release-week.md) purpose. Exceptionally for this release, the pre-release time will be more than just one week._

Done:
- Update README #286 
- Rename `attributes_for_faceting` into `filterable_attributes` #287 #292 
- Update `WaitForPendingUpdate` status #288
- Adapts tests according to v0.21.0 breaking changes #289
    - Rename fields `buildDate` into `commitDate`
    - Update `rankingRules`
    - `exhaustiveFacetsCount` return `False`
- Add missing tests according to new features #290
    - Phrase search tests
    - Filter/facet on number is now doable
    - Test the syntax on Filter array and string
- Update code sample file #291 #293

Co-authored-by: meili-bot <[email protected]>
Co-authored-by: Clémentine Urquizar <[email protected]>
Co-authored-by: Amélie <[email protected]>
Co-authored-by: alallema <[email protected]>