Test with CMake 3.10.2

Since https://github.com/Mbed-TLS/mbedtls-test/issues/262, cmake is CMake 3.20.2 or above everywhere on the CI. But in Mbed TLS 3.6 LTS, we claim compatibility with CMake 3.10.2.

The goal of this issue is to arrange to do at least some testing with CMake 3.10.2. It is available in all Docker images as cmake-3.10.2.

all.sh must still work if only cmake is available (as long as it's 3.10.2 or above). So for example, we can (in 3.6 only) check if cmake-3.10.2 exists, and make cmake a wrapper function if it does.