Update the FDC3 Charter document

[kriswest]

FDC3's Charter document (https://fdc3.finos.org/docs/fdc3-charter - whos content also appears at https://github.com/finos/FDC3/blob/Clarify-bridging-channel-sync-description/SCOPE.md) was written early in the creation of both FDC3 and the FINOS foundation and while FDC3's charter is well understood by the maintainers and long-term FDC3 participants, the document itself could be improved (feels like meeting notes from early FDC3 meetings). If asked what FDC3's charter is, most participants will quote the first line of the FDC3 introduction page (https://fdc3.finos.org/docs/fdc3-intro), which is not actually part of the charter document:

The mission of the Financial Desktop Connectivity and Collaboration Consortium (FDC3) is to develop specific protocols and taxonomies to advance the ability of desktop applications in financial workflows to interoperate in a plug-and-play fashion, without prior bi-lateral agreements.

The FDC3 Charter document should be rewritten to better serve its purpose of introducing new participants to the scope of FDC3.

This issue doesn't propose to change the scope of FDC3 (although it may have shifted slightly since its inception or should shift in the future), but rather to see the documentation of that charter improved.