Update documentation for ledger_entry Request

[ckeshava]

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1. The documentation does not mention "unexpectedLedgerType" error under the "Possible Errors" section. Here are examples of this error from the unit tests. This is the corresponding source code for the origin of the error message.
2. In case of parsing failures, API v1 returns a generic throw whereas API v2 returns invalidParams error. This recent change is coded here This difference in the behavior between v1 and v2 might need to specified in the docs page.

[ckeshava]

Under the "Possible Errors" section, "malformedDocumentID" needs to be documented. This error is returned for incorrectly specified Oracle ledger objects. This is the source code responsible for that error.