docs: translate V4-alpha documentation to Spanish (closes #603)

[intldds]

Description

Addressing issue #603, in which I've translated the V4-alpha documentation to Spanish.

This PR doesn't introduce a breaking change.

Related Issue(s)

Please link to the issue(s) here: #603

Other information

My process for translating the V4 docs was the following:

• Used DiffChecker to compare changes from V3 to V4-alpha docs;
• Used the Spanish V3 documentation as a template;
• Updated the documentation accordingly to the changes introduced;
• For technical words, I've made a translation of them the first time they appeared -- after that, I kept the original word for most of the times (eg. "nullifier", "scope", etc);
• I've updated the "sidebar" position of the translated docs accordingly to the position established in the V4-alpha documentation;
• I've also created the corresponding "json" files accordingly to the new docs.

Checklist

• My code follows the style guidelines of this project
• I have performed a self-review of my code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• My changes generate no new warnings
• I have added tests that prove my fix is effective or that my feature works
• New and existing unit tests pass locally with my changes
• Any dependent changes have been merged and published in downstream modules