feat: skip size json generation for targets in preview (RDT-733)

[fhrbata]

Targets in preview may not yet have support in esp-idf-size, which may cause a failure while the size json file is generated. This may block chip support team as they need to wait or work on the esp-idf-size support first.

This skips size json generation if target is in preview.

[fhrbata]

Tested locally with

idf-build-apps build -p ~/work/esp-idf/examples/get-started/hello_world/ -t esp32 --default-build-targets esp32 --size-file size_output.json --build-log idf_build_apps.log -v -v

vs esp32c5 which is in preview

idf-build-apps build -p ~/work/esp-idf/examples/get-started/hello_world/ -t esp32c5 --default-build-targets esp32c5 --size-file size_output.json --build-log idf_build_apps.log -v -v

[fhrbata]

Another, probably more accurate, approach could be to add option to esp-idf-size, which will dump supported targets and use this instead of PREVIEW_TARGETS

[hfudev]

@fhrbata Thank you for the PR. LGTM!