Add OPTIMADE version as an action parameter

[ml-evs]

As optimade-python-tools "latest" (v0.16.0) now tracks v1.1 of the OPTIMADE spec, setting all_versioned_paths to true now tests /v1.1 URLs. As well as the validator_version option, it could be useful to add optimade_version so that people can still use the validator action for v1.0.0. This will require a map from optimade-python-tools versions -> optimade version, so e.g. specifyting optimade_version: 1.0.0 will install the last supported OPT, v0.15.5.

[CasperWA]

I think I mentioned this at some point as well? Edit: Yup, this is #59. But let's make this supersede it.

Either we make it completely dynamic, crawling the github tags to try and determine the latest version with a desired version. But more practically I think we should find a way to make a bit "easier" to implement here? Maybe going as far as a static file. The issue there of course being that we'd need to update it everytime a new version is released of optimade.
Maybe we can make an action that does this? Either here or in the optimade-python-tools repo? I don't know.