Update software dependencies documentation

### Are there any linked Issues or Pull Requests?

_No response_

### Brief description

The documentation needs to be updated for the Summer 2026 release. The information would benefit from a re-organisation to make it obvious where specific software versions are mandatory and where they are merely indicative.

### Further details of the issue.

The current dependency information could benefit from being restructured into categories to separate

* general dependencies where the specific version is unimportant, e.g. python or netCDF
* tightly coupled dependencies, e.g. psyclone, where specific versions are required for particular releases of LFRic
* loosely coupled dependencies, e.g. YAXT, where we run and test with a particular version, but where other versions are also compatible

It would also be useful to include the dependency information for the last three (i.e. currently supported) releases.

We (SSD) need to add a pre-release task to our curation process to document the requirements for each new release ahead of partner testing.

Locate the current dependency documentation and the curation process used for pre-release work; no specific files or tests are named in the issue. Review the requirements for the last three supported releases, then reorganise the information into general, tightly coupled and loosely coupled dependencies and add the pre-release documentation task for Summer 2026.

Written by the indexing model from the issue text.