Add aiida-sssp-workflow plugin

[unkcpz]

To test preview pr from forked repo is working.

[github-actions]

PR Preview Action v1.4.5
🚀 Deployed preview to https://aiidateam.github.io/aiida-registry/pr-preview/pr-299/
on branch gh-pages at 2023-12-19 03:15 UTC

[ltalirz]

Very happy to finally see the sssp workflows available to everyone :-)

Some minor suggestions:

• add a pointer from https://github.com/aiidateam/aiida-sssp to the sssp-workflow plugin as well
• add a short description to the README of the aiida-sssp-workflow repo

e.g. like this section from the docs

These  workflows contain the verification of transferability (precision) and softness of the pseudopotentials. The precision of the pseudopotentials are measured by comparing the EOS of the solid-state calculation with the all-electron calculation.

The workflows run verification for pseudopotential convergence are for:

Delta factor:
Cohesive energy:
Phonon frequencies:
Bands distance:
Residual pressure: reflect the precision and the softness of the given pseudopotential

[unkcpz]

Thanks @ltalirz! Sure, I'll settle those and will make another release.
I should finish running all the verifications first, almost there ;)

This pr was to test the pr from fork will trigger the pr-preview, and it is there! Hope you don't mind that I directly merged #296 without approve. It has to be in the main first then the workflow action will take effect after.