Add ECSql Docs for querying by GUID

[ColinKerr]

querying by GUID is only covered in ECSql reference docs: https://www.itwinjs.org/learning/ecsqlreference/ecsqlfunctions/#strtoguid-guid-string

We should cover functions and bindGuid when it's a parameter.

These docs should be linked by docs on ways to find elements: #8739