Allow Generic frontend environment to regard 201 response as triggered deploy

Problem/Motivation

When using generic frontend environment the only allowed response status to consider a deploy triggered is 200.
There are some systems that, on the successful trigger of deploy, return status 201, which seems like a legitimate response because it means "Created".
If 201 is not accepted the new deployment never gets created and we are always stuck with the first deployment. In addition, the content changes never get cleaned, but stack forever as never deployed changes.

Steps to reproduce

Create a generic frontend environment with a hook from a system that returns status 201 on successful trigger of deployment (example: vercel).
Change some content.
Trigger a deployment for this environment.
There is a warning message "created".
The deployment is not processed, there is no new deployment, but the first deployment is still there with all the old changes.

Proposed resolution

Allow response status 201 in the FrontendEnvironmentBase. 201 seems legitimate for the particular task of checking whether the deployment was triggered. This is allowed in build_hooks_bitbucket as well.

Remaining tasks

User interface changes

API changes

Data model changes