Add devcontainer containing essential build tools for S-CORE

[lurtz]

For CI container images shall be small so that CI is fast. However for developers we usually want more tools to increase productivity.

TODO

• use image in developer devcontainer
• remove duplicated code

[lurtz]

As as I build using a builder created with docker buildx create, the devcontainer build cannot find the already build buildcontainer image, which was done one step before. Using the default builder it works.

Therefore I put this on hold, because I think it might not be worth the effort. At the moment the v1.1.0 version of the container needs 37s to come up in CI. Its size is 4.3GB. Total build time was 6 minutes and the build time of the communication repo is 12 minutes.

Further information information I found about this issue:

• Support dependencies when using bake docker/buildx#447
• https://github.com/docker/buildx/blob/v0.8.0-rc1/docs/reference/buildx_bake.md#using-a-result-of-one-target-as-a-base-image-in-another-target

Here I doubt that I can pass the proper buildx options down via devcontainercli.

If we ever want to have a dedicated image for CI, maybe it is easier to store the devcontainer features in a separate repository and use those. It is not possible to reuse local features.