source_audio.json schema missing channel symbols for "SGRP" and "222" groups from ST 2110-30

[andrewrscott]

The source_audio.json schema includes an enum list of audio channel "symbol" strings which are taken from from VSF TR-03 Appendix A per the description. For the most part, the symbols match to each of the possible channel grouping symbols listed in Table 1 of ST 2110-30, but there are two holes:

1. There are no channel symbols defined for the group symbol "SGRP" (SDI audio group)
2. The channel symbols for the "222" group (22.2 Surround) are listed in ST 2036-2 Table 1, but are not included in the IS-04 schema.

[garethsb]

Agreed

Cf. https://github.com/sony/nmos-cpp/blob/85d5443c0e41ba45d44a7ba9da66e8deceaf9955/Development/nmos/channels.h#L110-L111