doc: Use EXTRA_CONF_FILE in .rst/.md files

[butok]

Use EXTRA_CONF_FILE in documentation .rst/.md files, that replaced deprecated OVERLAY_CONFIG since the Zephyr v3.4 release.

[JarmouniA]

@butok What a coincidence :) I prepared a similar PR 2 days ago that deals with this in testcase.yaml & sample.yaml files. Will send it this evening.

Edit: I just saw #79504 when I rebased my branch 👀 Still have some tweaks to upstream (#80083).

[butok]

@butok What a coincidence :) I prepared a similar PR 2 days ago that deals with this in testcase.yaml & sample.yaml files. Will send it this evening.

Edit: I just saw #79504 when I rebased my branch 👀 Still have some tweaks to upstream (#80083).

Thank you,

The current Zephyr approach for deprecated code is problematic. It results in new and legacy code continuing their lives independently. People copy and paste without knowing it is deprecated.

Proposal: If something is deprecated, it should be marked as deprecated in the source code (compile error/warning) and should be removed entirely in a future release.