Support rendering of compound linked credentials

There's several examples of complex compound credentials (LER-RS resumes, CLRv2, etc) that embed many VCs in an "outer" container credential. Example of an app that produces a compound LER-RS credential: https://resume.allskillscount.org/

BUT, a complementary, and possibly preferable, approach (brought up by @paulfdietrich and the DB folks) is to model compound credential as an outer container credential with LINKS (secured by digest hash) to other VCs in a presentation.

This issue is -- how to indicate that a renderMethod template is intended to include these linked credentials? So, for example, if you have an LER-RS credential, which includes 3 VCs (linked to them, with digest hash), do we need any special affordances in the renderMethod section that says "also include those linked VCs when rendering this template?"

Review the LER-RS and CLRv2 examples, the linked-VC presentation approach, and the renderMethod section described in the issue. Done means deciding and documenting whether renderMethod needs an explicit way to include linked credentials when rendering a compound credential.