Add challenge password to CSR mbedtls 3.6

[rgqsch]

Description

New code based on an older PR, fixed to latest coding styles. This will add a challenge password to the CSR which might be needed by some SCEP servers

PR checklist

Please remove the segment/s on either side of the | symbol as appropriate, and add any relevant link/s to the end of the line. If the provided content is part of the present PR remove the # symbol.

• [ ] changelog provided in this PR
• [ ] development PR provided #10431
• [ ] TF-PSA-Crypto PR not required because: Not changed
• [ ] framework PR provided Mbed-TLS/mbedtls-framework#219
• [ ] 3.6 PR provided in this PR
• tests provided In this PR

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[mpg]

Thanks for creating a 3.6 backport! However, I should point out that 3.6 is an LTS branch and normally only receives fixes (bugs & vulnerabilities), while this looks like a new feature.

[rgqsch]

Thanks for creating a 3.6 backport! However, I should point out that 3.6 is an LTS branch and normally only receives fixes (bugs & vulnerabilities), while this looks like a new feature.

It is a new feature, we work on 3.6 atm, and tought I might share this addition.