References to specific versions of the stats schema is incorrect

[mattheworiordan]

In our stats docs, such as https://ably.com/docs/metadata-stats/metadata/subscribe#stats-format, we link to a specific version of the schema https://schemas.ably.com/json/app-stats-0.0.1.json.

From @SimonWoolf :

The docs shouldn't hardcode what version to expect, that defeats the point of having a schema field in the struct.
We should have a versionless url that points to the latest version that the docs can link to for the current version (but make it clear that the one linked from the schema field of a stats object is definitive for itself)

Latest version at the time of writing this is 0.0.5.json, see https://schemas.ably.com/json/app-stats-0.0.5.json.

This applies to the control API as well, and accounts and apps.