doc: develop: manifests: external: add wolfSSL

[night1rider]

Add documentation about using wolfSSL as an external module.

[kartben]

@night1rider Thanks a lot for the contribution! Looks pretty good already but adding a few comments + waiting for CI to build the docs to also eyeball the rendered page (it will be available at https://builds.zephyrproject.io/zephyr/pr/98238/docs/develop/manifest/index.html)

Note that you will also need to use your legal name as commit author and in the signed-off-by entry - thanks!

[kartben]

you need to properly set the git author too! thanks :)

git commit --amend --author="Z... B... <[email protected]>" --no-edit

[night1rider]

compliance check had an issue with the single back tick, updated to use the double back tick as mentioned in the error log

[sonarqubecloud]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarQube Cloud

[kartben]

compliance check had an issue with the single back tick, updated to use the double back tick as mentioned in the error log

Oops of course, sorry!