Accepts "1" for a boolean

This issue has been migrated from [#10497](https://github.com/matrix-org/synapse/issues/10497).

---

When the matrix specification says a type is a boolean, synapse accepts both `0`, `1`, `false` and `true` in the request, while only `false` and `true` are valid values.

I've seen this behaviour in at least the typing API (https://github.com/matrix-org/sytest/pull/1088) and the register API (https://github.com/matrix-org/sytest/pull/1089)

Start with the typing API and register API request handling, then compare their boolean validation with the Matrix specification. Review the related sytest coverage referenced in PRs #1088 and #1089. Done means invalid numeric boolean values are rejected while the specified boolean values remain accepted in both APIs.

Written by the indexing model from the issue text.