shorten project k8s namespace name

[lionelB]

It would be nice to have shorter namespace name for

- code-du-travail-numerique-51-build-k8s-deploy-0nialh
+ cdtn-build-k8s-deploy-0nialh

[douglasduteil]

🤔 We might have gitlab conflicts if we alter the namespace names.
To confirm with https://docs.gitlab.com/ee/user/project/deploy_boards.html
But that my be irrelevant if the namespace is created through a GitHub pipeline
\cc @gary-van-woerkens

[lionelB]

cdtn-51-build-k8s-deploy-0nialh is ok too

[lionelB]

also
why url of master is
https://master-dev-code-du-travail-numerique.dev2.fabrique.social.gouv.fr/ is when preprod is https://preprod-code-du-travail-numerique.dev2.fabrique.social.gouv.fr/

(master-dev) vs preprod.
why it's not simply master ?