Missing wallet views endpoints and response data

[hgrano]

The following contracts are queried in the UI but are not available through the wallet views API. Currently, they are retrieved via the JSON API instead:

• Settlement OpenOffer and OneTimeOffer (new endpoints should be added for these)
• Instrument Metadata (can add the Metadata view as an optional field within the instruments API response)
• Disclosure interface views could also be added in responses for some endpoints such as the holdings, instruments and metadata. This could be incorporated into these existing endpoints, but just add an extra field in the response for the disclosure view
• Fetch by contract ID: it would be useful to be able to fetch contracts by their ID using wallet views, but not strictly necessary e.g. a fetch Holding by ID endpoint which would return a single HoldingSummary response