rego-v1: Document and report on alternatives to calls to deprecated built-ins

[johanfylling]

In the docs, a section should be added where, for each deprecated built-in, an alternative function call or snippet of Rego is described.

When running opa check and opa fmt with the --strict or --rego-v1 flags, the errors produced by calls to deprecated built-ins should be decorated with links to the above, relevant documentation.

This could serve as a replacement for #6445. Or, we could opt to only rewrite certain special cases in 6445; defaulting to the more detailed error reporting described in this issue.