[DOCS] Update links for operator definitions

[VinceNeede]

Description

Updated link refs in documentation of SiteType

Fixes #1626

How Has This Been Tested?

I've run make_local_notest.jl and checked that the new links worked.

Checklist:

• My code follows the style guidelines of this project. Please run using JuliaFormatter; format(".") in the base directory of the repository (~/.julia/dev/ITensors) to format your code according to our style guidelines.
• I have performed a self-review of my own code.
• I have commented my code, particularly in hard-to-understand areas.
• I have added tests that verify the behavior of the changes I made.
• I have made corresponding changes to the documentation.
• My changes generate no new warnings.
• Any dependent changes have been merged and published in downstream modules.

[mtfishman]

Thanks!