feat(serial_uart): adds Serial (UART) documentation (#11993)

* feat(serial_uart): adds main Serial documentation

* feat(serial_uart): improves Serial documentation

* fix(serial): fixes example session headers

Removed redundant section headers for example applications.

* fix(serial): docs refer to ESP-IDF instead of IDF

* fix(serial): restores necessary example reference

* ci(pre-commit): Apply automatic fixes

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Co-authored-by: pre-commit-ci-lite[bot] <117423508+pre-commit-ci-lite[bot]@users.noreply.github.com>

Author: SuGlider