Missing support for RDDs

[fschleich]

I recommend we consider clarifying that "Public CD" can refer to both Committee Drafts and Pre-TC-Ballot RDDs that are made available to the public. Additional tweaks will be necessary and I'd be happy to propose specific changes if there's general support for extending the scope.

More Context:
AG-22 only describes a process for SMPTE Engineering Documents, but there's also a desire to use the Public CD process for RDD projects. In fact, the first TSP document was a specialization of RDD 45 - IMF Application ProRes (i.e. the document type was not necessarily chosen to have "full control" over the content of the document, but rather because of the need to reference existing RDDs). The TSP in question was eventually converted into PCD RDD 59-1 [1].

[1] https://github.com/SMPTE/rdd59-1

TSP projects were assigned the "TSP" doc type from the start, so there was no differentiation between "ST" and "RDD". While documents could be drafted as Standards and only be converted to RDDs following the Public CD period, that would inevitable cause confusion throughout the process (e.g. project review comments about referencing RDDs, confusion during PCD on whether the document will eventually become an ST or RDD, etc).