wolfHSM: add DTLS client example that uses HSM as cryptographic back end

[rizlik]

No description provided.

[bigbrett]

@rizlik sorry for delay on this. Pls resolve merge conflict

[padelsbach]

@rizlik, can you please resolve the conflicts?

[Copilot]

Pull request overview

This PR introduces a new hsm/ area to the examples repository, adding a DTLS client example that demonstrates using wolfHSM as the cryptographic backend (keeping private key operations on the HSM), and wires the new area into the top-level documentation.

Changes:

• Added a new hsm/ documentation entry and an hsm/README.md landing page for wolfHSM-related examples.
• Added a DTLS client example (hsm/dtls_client/) including build/run tooling (Makefile) and required wolfSSL/wolfHSM configuration headers.
• Implemented a DTLS client that offloads ECC signing to wolfHSM via PK callbacks.

Reviewed changes

Copilot reviewed 7 out of 7 changed files in this pull request and generated 3 comments.

Show a summary per file

File	Description
README.md	Adds a new “HSM” section to the top-level directory listing.
hsm/README.md	Introduces wolfHSM examples landing documentation and a quick-start.
hsm/dtls_client/Makefile	Provides build/run automation, including cloning wolfSSL/wolfHSM and building the DTLS client + servers.
hsm/dtls_client/README.md	Documents build/run steps and architecture for the DTLS client example.
hsm/dtls_client/user_settings.h	Supplies wolfSSL user settings needed for DTLS + crypto-callback/HSM integration.
hsm/dtls_client/wolfhsm_cfg.h	Sets wolfHSM compile-time configuration for the DTLS client example.
hsm/dtls_client/wh_dtls_client.c	Implements the DTLS client using wolfHSM for ECC signing operations.

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