Further clarification of Instrument Dictionary IDs

Originally brought up by @lspiro-Tick42 during an FDC3 call.

While ISIN, SEDOL etc might be somewhat self-explanatory, it would be beneficial if we could specify further what exactly what data items should be used for the different ID types. Eg "BBG" doesn't really clarify if it should be the "Bloomberg Terminal Symbol" or the "BPod Symbol".

Ideally I think these items should be specified by the provider or owner of the individual symbology scheme but as a start I think it makes sense if we document our thoughts and thus drive adoption and standardization that way.

A great topic for our next call and for us to form a subgroup to focus on this.

Start by reviewing the Instrument Dictionary ID definitions and the examples in the issue, especially the ambiguity around “BBG” data items. Discuss the proposed clarifications in the next call or with the subgroup mentioned in the issue; done means documenting agreed provider or owner-specific data items for each ID type.

Written by the indexing model from the issue text.