Merge test dependencies into main Project.toml and fix documentation link

- Combine test/Project.toml into main Project.toml using [extras] and [targets]
- Add compat constraints for all test dependencies
- Fix broken external reference in docs/src/manual-model.md
- Update version to 1.1.7-beta

Author: ocots

Project.toml

@@ -1,7 +1,7 @@
 name = "OptimalControl"
 uuid = "5f98b655-cc9a-415a-b60e-744165666948"
 authors = ["Olivier Cots <olivier.cots@toulouse-inp.fr>"]
-version = "1.1.7"
+version = "1.1.7-beta"
 
 [deps]
 ADNLPModels = "54578032-b7ea-4c30-94aa-7cbd1cce6c9a"