Update API docs

[liammulh]

As of today (December 8th, 2023), here's what I see when I go to https://docs.civicdb.org/en/latest/api.html:

In April 2022 CIViC V2 was launched, which includes a new GraphQL API. The old API is still available at v1.civicdb.org/api. It accesses a frozen datadump and does not include any new data since the switchover. While we expect the V1 API to be accessible for a few more months (deprecation date forthcoming) any new integrations should use the V2 API and existing integrations should switch to the V2 API as soon as possible. Please contact us at help@civicdb.org for assistance.

It looks to me like v1.civicdb.org is timing out:

> curl -o - -I https://v1.civicdb.org/api/variants/13
curl: (28) Failed to connect to v1.civicdb.org port 443 after 75108 ms: Couldn't connect to server

If this is intentional, then the docs should be updated to say that the v1 API is no longer available, and that at this point everyone should be using the v2 API.