arrow

GH-40799: [Doc][Format] Implementation status page should list canonical extension types (#41053)

### Rationale for this change

Two specifications and one implementation of canonical extension types were added and this should be documented.

### What changes are included in this PR?

This represents current state of canonical extension types.

### Are these changes tested?

No, docs only.

### Are there any user-facing changes?

In so much as they read docs.
* GitHub Issue: #40799

Authored-by: Rok Mihevc <rok@mihevc.org>
Signed-off-by: Rok Mihevc <rok@mihevc.org>