Release 3.6.2 with 3.6.1 + the pkwrite patch

[gilles-peskine-arm]

Release candidate for Mbed TLS 3.6.2, indented to be used without a complicated history. Cherry-picks just the bug fix from https://github.com/Mbed-TLS/mbedtls/pull/9691, plus a changelog entry, plus a version bump and David's documentation update from https://github.com/Mbed-TLS/mbedtls/pull/9692.

CI jobs: ~Internal CI, OpenCI~ OpenCI (new Brainpool test cases commented out) OpenCI (-O2 instead of -O3 for GCC+Asan builds)

PR checklist

• [x] changelog provided | not required because:
• [x] development PR https://github.com/Mbed-TLS/mbedtls/pull/9690
• [x] framework PR not required
• [x] 3.6 PR here
• [x] 2.28 PR not required because: 2.28 not affected
• tests provided