API: provide new suggested individual id

[vkirkl]

Several UI locations allow for the assignment of a new individual id (including Encounter details | Identity, Match page | confirm no match -> new individual dialog). There are some legacy (and possibly inconsistent) approaches to suggest new ids based on location, project, and perhaps moon phase.
Let's start by creating and documenting a single individual id suggestion API end point that deterministically returns a suggestion and can be used by the Encounter and Match pages. The first iteration of this need not use project data since that will likely be re-architected in 10.11.

First use case will be for #1338
This should address #1195