Bundling SpineOpt and Julia installation inside Toolbox

[nelliputkonen]

To ease the installation process for someone who is starting to use SpineOpt (for example, we have 30 student next spring at Tampere University who will have to install SpineOpt), it would be most convenient if the currently manual steps of installing and finding Julia and then installing SpineOpt could be bundled into single "Install SpineOpt" step within Toolbox, that would configure Julia installation in the background. If at all possible, the installation could further include downloading a template SpineOpt workflow + template database (see SpineOpt issue https://github.com/spine-tools/SpineOpt.jl/issues/1022 on improving installation instructions and adding a ready workflow and template database to start out with).

See discussion on issue https://github.com/spine-tools/Spine-Toolbox/issues/2797. If the approach suggested above is taken, then it would mean closing the linked issue with option 3: Hide Install Julia button.

As additional ideas, this could also be implemented for other tools, at least FlexTool...?