Add a separate nightly build workflow

[dipinknair]

📝 Description of the feature

Currently, the nightly run is part of the same CI/CD workflow. However, it would be beneficial to isolate it specifically for running embedding and remote tests. In this way documentation style check , code style check can be skipped. Additionally, more actions, such as removing untagged Docker images, can be incorporated into the nightly run.

💡 Steps for implementing the feature

Untagged images should only be cleaned once in a week so that it's easier to identify the failing changes.

🔗 Useful links and references

for removing untagged docker images refer - https://github.com/ansys/pymapdl/blob/main/.github/workflows/docker_clean_untagged.yml