* Add namespcace ID attribute
This commit also introduce `id` comouted value which is numeric value
used by GitLab to iteract with repository. This should simplify use of
`gitlab_project_hook` usage and would allow to introduce other resources
as described in #14471
* Fixes requested by @richardc
* Handle optional `namespace_id`
Here we add a new resource type `gitlab_project_hook`. It allows for
management of custom hooks for a gitlab project.
This is a relatively simple resource as a project hook is a simple
association between a project, and a url to hit when one of the flagged
events occurs on that project.
Hooks (called Webhooks in some user documentation, but simply Hooks
in the api documentation) are covered here for users
https://docs.gitlab.com/ce/user/project/integrations/webhooks.html and
in the API documentation at
https://docs.gitlab.com/ce/api/projects.html#hooks
Łukasz Jan Niemier