chainHead_storage: Backport queries for value types (#14551)

* chainHead/events: Add storage params and events

Signed-off-by: Alexandru Vasile <alexandru.vasile@parity.io>

* chainHead/tests: Check storage events serialization / deserialization

Signed-off-by: Alexandru Vasile <alexandru.vasile@parity.io>

* chainHead/error: Add error for invalid WaitForContinue storage call

Signed-off-by: Alexandru Vasile <alexandru.vasile@parity.io>

* chainHead/storage: Use new items params

Signed-off-by: Alexandru Vasile <alexandru.vasile@parity.io>

* chainHead/tests: Adjust storage tests to the new API

Signed-off-by: Alexandru Vasile <alexandru.vasile@parity.io>

* chainHead/events: Generalize StorageQuery by provided key

Signed-off-by: Alexandru Vasile <alexandru.vasile@parity.io>

* chain_head: Add dedicated ChainHeadStorage client for queries

Signed-off-by: Alexandru Vasile <alexandru.vasile@parity.io>

* chainHead/storage: Implement queries for hashes of values

Signed-off-by: Alexandru Vasile <alexandru.vasile@parity.io>

* chainHead/tests: Check storage queries for hashes of values

Signed-off-by: Alexandru Vasile <alexandru.vasile@parity.io>

* chainHead: Improve API documentation wrt multiple entries

Signed-off-by: Alexandru Vasile <alexandru.vasile@parity.io>

* chainHead/event: Rename StorageQueue ty to queue_ty

Signed-off-by: Alexandru Vasile <alexandru.vasile@parity.io>

* chianHead: Add helper to encode chainHead results as hex str

Signed-off-by: Alexandru Vasile <alexandru.vasile@parity.io>

* Update client/rpc-spec-v2/src/chain_head/error.rs

Co-authored-by: Sebastian Kunert <skunert49@gmail.com>

* chainHead: Change the `queryResult` to a plain `Result`

Signed-off-by: Alexandru Vasile <alexandru.vasile@parity.io>

* chainHead: Stop producing events after the first error

Signed-off-by: Alexandru Vasile <alexandru.vasile@parity.io>

* chainHead: Change child_key to child_trie API param

Signed-off-by: Alexandru Vasile <alexandru.vasile@parity.io>

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Signed-off-by: Alexandru Vasile <alexandru.vasile@parity.io>
Co-authored-by: Sebastian Kunert <skunert49@gmail.com>