Clarify `TransferStartMessage` by consumer

[ndr-brt]

Feature Request

In the transfer process binding there's this statement:

DataspaceProtocol/specifications/transfer/transfer.process.binding.https.md

Lines 106 to 107 in 0b7ac40

	The [=Consumer=] can POST a [Transfer Start Message](#transfer-start-message) to
	attempt to start a [=Transfer Process=] after it has been suspended:

that makes total sense, this is not backed up by proper details in the protocol file, where it looks like the TransferStartMessage can only be sent by the provider:

DataspaceProtocol/specifications/transfer/transfer.process.protocol.md

Lines 130 to 151 in 0b7ac40

	### Transfer Start Message
	| | |
	|---------------------|--------------------------------------------------------------------------------------------|
	| **Sent by** | [=Provider=] |
	| **Resulting state** | `STARTED` |
	| **Response** | [ACK](#ack-transfer-process) or [ERROR](#error-transfer-error) |
	| **Schema** | [JSON Schema](message/schema/transfer-start-message-schema.json) |
	| **Example** | [Message](message/example/transfer-start-message.json) |
	| **Properties** | <p data-include="message/table/transferstartmessage.html" data-include-format="html"></p> |
	The Transfer Start Message is sent by the [=Provider=] to indicate the data transfer has been initiated.
	- The `dataAddress` MUST be provided if the current transfer is a pull transfer and contains a transport-specific
	endpoint address for obtaining the data. The kind of transport is signaled by the `endpointType` property which
	determines a set of REQUIRED `endpointProperties` in a [=Profile=] separate from this specification.
	- The `endpointProperties` MAY (among others) contain the following OPTIONAL values:
	- `authorization` - An opaque authorization token that clients MAY present when accessing the transport-specific
	endpoint address.
	- `authType` - The auth token type. For example, the value MAY be `bearer`. If present, this value MAY be used in
	conjunction with transport rules to define how the client MAY present an authorization token.

Which Areas Would Be Affected?

transfer process protocol