Proposed updates for IETF 113

[italobusi]

Prepare and update I-D to be presented at IETF 113:

• [x] Add IANA Considerations: Fix #12
• [x] Add WDM path constraints: fix #15
• [x] Add optical impairments constraints: fix #14
• [x] Add Acknowledgements: fix #3

Pending merge of PR:

• [x] https://github.com/ietf-ccamp-wg/ietf-ccamp-layer0-types-ext/pull/36

[italobusi]

If we look at the current flex grid and wson path computation - they are identical. Therefore I think a better strategy is to combine these two and have a common path computation model for both flex grid and wson. We can add flex-grid- or wson-specific constructs onto the common model using augments (or even within the same model by switch-case statement) if there is a need.

Let's discuss this comment in the context of issue #9 since this has an impact on the number of documents that we should progress for optical path computation