Fix `MultiSearch` functionality (elastic#8176) (elastic#8178)

- Implement `IStreamSerializable` for array request descriptors
- Do not automatically infer index for optional `Indices` parameters

Co-authored-by: Florian Bernd <[email protected]>

Fix index inference for requests with `index`/`indices` parameter (el…

…astic#8170) (elastic#8172)

Co-authored-by: Florian Bernd <[email protected]>

Fix `BucketsPath` (de-)serialization (elastic#8164) (elastic#8166)

Co-authored-by: Florian Bernd <[email protected]>

Generate inference constructor overloads (elastic#8159) (elastic#8161)

Co-authored-by: Florian Bernd <[email protected]>

Fix union serialization (elastic#8146) (elastic#8148)

Co-authored-by: Florian Bernd <[email protected]>

Add missing obsolete attributes (elastic#8137) (elastic#8139)

Co-authored-by: Florian Bernd <[email protected]>

Regenerate client using the latest spec (elastic#8129) (elastic#8131)

Co-authored-by: Florian Bernd <[email protected]>

Fix serialization of `MultisearchBody`/`MultisearchHeader` (elastic#8107

) (elastic#8111)

Co-authored-by: Florian Bernd <[email protected]>

Re-implement `Exists` property (elastic#8102) (elastic#8104)

Co-authored-by: Florian Bernd <[email protected]>

Reintroduce fluent API for `RangeQuery` (elastic#8098) (elastic#8100)

Co-authored-by: Florian Bernd <[email protected]>