Update default MbedTLS version to v3

For more than a year now, S2OPC is compatible with MbedTLS revision 2.28 (default) and MbedTLS revision 3.x (to be deployed on Zephyr).

Since:

• MedTLS revision 2.28 security maintenance is over at the end of 2024
• MedTLS revision 3.6 LTS release note is very promising regarding performance and features (see https://github.com/Mbed-TLS/mbedtls/releases)
• S2OPC compatibility with the two revisions of MbedTLS incudes code complexity

Switching the default revision of MedTLS in S2OPC to V3.6 shall be considered.

Note RBA:

• Finally switching to the last version of MbedTLS which is the v3.6.2
• Missing MbedTLS v3 for Zephyr until zephyr v7 LTS is available for S2OPC.
• Missing MbedTLS v3 for FreeRtos as STM32CubeH7 package does not support mbedtls v3.