Fix or replace links to ably/docs content that was outside content/client-lib-development-guide

[QuintinWillison]

As pointed out by @lawrence-forooghian in #1 (comment):

The link resolves relatively and directs visitors to non-existent location at sdk.ably.com:

https://sdk.ably.com/api/rest-api#update-device-registration

When it should be to:

https://docs.ably.com/api/rest-api/#update-device-registration

We could fix this in the textile documents in this new home, or we could do some processing on the textile to replace a subset of relative URLs with absolute URLs. The latter approach there has the advantage that it keeps our textile document commit history cleaner, however at the loss of 'correctness' and an increase in 'speciality' of our processing. 🤔

[lawrence-forooghian]

I think that if we keep it within a single well-explained commit, a one-time edit wouldn't be much of a problem.

[sync-by-unito]

➤ Automation for Jira commented:

The link to the corresponding Jira issue is https://ably.atlassian.net/browse/SDK-2837