### What?
Update `SelectFieldBaseClientProps` type so `value` accepts `string[]`
for `hasMany` selects
### Why?
Multi-selects currently error with “Type 'string[]' is not assignable to
type 'string'”.
### How?
- Change `value?: string` to `value?: string | string[]`
- Also adds additional multi select custom component to `admin` test
suite for testing
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Co-authored-by: Jarrod Flesch <jarrodmflesch@gmail.com>