feat: support web hotfixes via custom repo/branch

[aldbr]

This PR aims at installing a custom diracx-web coming from another repo/branch. This would allow us to easily hotfix it if required.

Before going further, I just want to make sure that I am going in the right direction. Currently, web-container-entrypoint does not work because git is not installed in the image I am using (node:alpine). I guess I should add a custom image in https://github.com/DIRACGrid/container-images, shouldn't I?

[chrisburr]

I think having web-container-entrypoint might get a bit painful as we have to also synchronise the node version with the webapp code.

Could we have two init containers use secret-generation to clone the code in to an emptyDir and then build the sources in a second container?

[aldbr]

Now there are 2 init containers:

• clone-diracx-web (use secret-generation): clone the repo and the specific branch in a volume. There is https://github.com/DIRACGrid/container-images/pull/9 to install git in the secret-generation image. For now, I just install it within the init container: https://github.com/DIRACGrid/diracx-charts/pull/77/files#diff-852c1e93c121b0d150d98fa58b3059b5f689e92f7fe55226cbf24296deca45beR68
• install-diracx-web (use the node image provided in values.yaml): build the package and store the static files in another volume

And then the static files are mounted to the diracx-web production container in place of the original production static files.