Add RawValue support for non-converted Payloads

[THardy98]

What was changed

Added RawValue support for non-converted Payloads - a thin wrapper around Payload.

RawValue is intended to be used for payloads that bypasses normal payload conversion. It uses the presence of the METADATA_RAW_VALUE_KEY in its payload's metadata to determine if the payload bypasses normal payload conversion or not.

It has a minimal API, useful for custom data converters that use RawValue, including:

• send: to be used when sending the RawValue to the server (i.e. toPayload)

send adds metadata to its payload that identifies it as a RawValue.
This metadata (METADATA_RAW_VALUE_KEY) is used to check whether a payload is a RawValue on arrival.

This metadata should be checked before you...

• receive: to be used a payload you expect to be a RawValue from the server (i.e. fromPayload)

receive strips the raw value metadata and constructs a RawValue

This is a different approach to how this was implemented in other SDKs as TS does not include type hints or similar when converting from a payload back to its original representation. As such, we use the payload metadata to give us a hint.

---

Also modified the existing built-in metadata query to return a RawValue (formerly returned the metadata proto object). This is not backwards compatible, existing users of this query (principally UI and CLI) will need to convert the payload from the RawValue (see example in the test).

1. Closes [Feature Request] Support "RawValue" non-converted values #1629, [Feature Request] Built-in query responses should use "RawValue" #1630

2. How was this tested:
   Added short integration test, modified the existing built-in metadata test.

3. Any docs updates needed?
   Possibly. Maybe for the change to the built-in metadata query.