Strict enforcement of allowed link types

[fredjn]

Applicable Issues

Fixes #347

Description of the Change

This patch adds an enum of allowed link types to all the event schemas

Alternate Designs

None

Benefits

Makes it harder to misuse the protocol, and to create/send events with improper link types.

Possible Drawbacks

The change might break services that implement validation but currently send events with arbitrary link types.

Sign-off

Developer's Certificate of Origin 1.1

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Signed-off-by: Fredrik Fristedt <[email protected]>

[fredjn]

I just realized that the schemas are generated. I will revise the PR with a commit to cater for that instead.

[fredjn]

This became a bit more problematic than I first anticipated, holding off a bit until I have had time to discuss with someone from TC.

[fredjn]

As it happens this had already been reported and denied(?) - Ref. #148