task: register w3id.org redirects for w3c-ccg.github.io URLs, and update links in registry to use w3id.org URLs

[bnewbold]

The task is to go through the "Decentralized Identifier Core Registries" doc (index.html in this repo), identify relevant URLs to w3c-ccg.github.io, register w3id.org permanent URLs (redirects) following the process at https://w3id.org/#new, and then update the registry doc to use the permanent URLs instead of direct github URLs. See context below for background and motivation.

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Copying conversation from #525.

@OR13 said:

You could change this as well...
... https://w3id.org/security/suites/secp256k1-2019
confusing to see https://w3c-ccg.github.io/lds-ecdsa-secp256k1-2019/ point to a different place.... that would need to be fixed in perma-id repo.

@bnewbold replied:

Not sure I understand what you are proposing here. Almost all of the other "Normative Definition" column links under "6.1 Verification method types" are https://w3c-ccg.github.io/... URLs, not https://w3id.org/... URLs.
If those "should" also be w3id.org links instead, i'd do that all in a separate PR to keep this PR small and simple.

@OR13 replied:

Yes, agreed... I am pointing out that w3id.org is redirecting to those github pages repos... and that its therefore safer (from a long term link perspective, to assume w3id.org will outlast github, other wise we would not be using it).
In either case, you can't fix this here... you would need to open PRs on w3id.org first, and then come here to update the links that are currently to github.
We did get objections related to linking directly to github in previous reviews from W3C.

@TallTed replied:

All the w3c-ccg.github.io links should be replaced by w3id.org links that redirect to the w3c-ccg.github.io location today, and are expected to be redirected to w3c.org/TR at some point. The point of the w3id.org links is that they will not need to change between Drafts and Recs, so anyone who implements based on these links will not have to change anything when we relocate (for instance, when we transition from Draft to Rec) the specs. On the other hand, anyone who implements based on the w3c-ccg.github.io links will have to change things anytime we transition from Draft to Rec or otherwise relocate the docs.