Standalone devcontainers for all MAS projects

Currently devcontainers are not working properly (see also https://github.com/OWASP/mas-website/pull/79).

mas-website is the only repo that has a devcontainer, and it requires that the sibling projects masvs, maswe and mastg be manually checked out previously. But they are not mounted into the container.

I propose a stable environment based on the image mcr.microsoft.com/devcontainers/base:trixie which uses mounted images for the sibling projects.

This works for four MAS projects. So it is not relevant which one the developer is working on. And since we use mounted images, we can reuse the checkouts.

Examples:

• If I work on mas-website, devcontainer will mount masvs, maswe and mastg as an image and mount the source into /workspace/mas-website
• If I work on mastg, devontainer will mount masvs, maswe and mas-website as an image and mount the source into /workspace/mastg.

In both cases, the server is started from the /workspace/mas-website.

I tried to reuse as much code as possible in the mas-website project, since it is required by all, but the Dockerfile, which contains the requirements for pip install, is shared across all four projects.

There are four PRs, one in each project. They should be merged simultaneously since they depend on each other.

Please let me know if you have suggestions.

Start by reviewing the existing devcontainer in mas-website and the shared Dockerfile requirements, then compare the corresponding setup across masvs, maswe, and mastg. Done means each of the four projects can use the stable base image, mount sibling checkouts, and start the server from /workspace/mas-website.