Cogeo-mosaic

* update morecantile requirement to >= 3.0
* update rio-tiler requirement to >= 3.0 and update Backend's properties
* switch from `requests` to `httpx`
* add `BaseBackend.assets_for_bbox()` method (https://github.com/developmentseed/cogeo-mosaic/pull/184)

**breaking changes**

* remove `BaseBackend.metadata()` method (can be replaced by `BaseBackend.mosaic_def.dict(exclude={"tiles"})`)
* remove `cogeo_mosaic.models.Metadata` model
* remove python 3.6 support
* `BaseBackend.path` -> `BaseBackend.input` attribute (`input` was added in rio-tiler BaseReader)

* Add Google Cloud Storage (`gs://...`) mosaic backend (author AndreaGiardini, https://github.com/developmentseed/cogeo-mosaic/pull/179)

* Make sure to pass an openned file to click.Progressbar (https://github.com/developmentseed/cogeo-mosaic/pull/178)

* update rio-tiler version dependencies
* update pygeos dependency to >=0.10 which fix https://github.com/developmentseed/cogeo-mosaic/issues/81

**breaking**

* `gzip` is now only applied if the path endswith `.gz`
* remove `backend_options` attribute in base backends. This attribute was used to pass optional `gzip` option and/or STAC related options
* STAC backends has additional attributes (`stac_api_options` and `mosaic_options`)

* add `SQLite` backend (https://github.com/developmentseed/cogeo-mosaic/pull/148)
* fix cached responsed after updating a mosaic (https://github.com/developmentseed/cogeo-mosaic/pull/148/files#r557020660)
* update mosaicJSON.bounds type definition to match rio-tiler BaseReader definition (https://github.com/developmentseed/cogeo-mosaic/issues/158)
* add default bounds/minzoom/maxzoom values matching the mosaicjson default in the backends (https://github.com/developmentseed/cogeo-mosaic/pull/162)
* raise an error when trying to pass `mosaic_def` in read-only backend (https://github.com/developmentseed/cogeo-mosaic/pull/162)
* add `MemoryBackend` (https://github.com/developmentseed/cogeo-mosaic/pull/163)

**breaking**

* Updated the backends `.point()` methods to return a list in form of `[(asset1, values)]` (https://github.com/developmentseed/cogeo-mosaic/pull/168)