feat(*.yml): add license to all files

[Wabri]

Closes #777

I use find+sed:

find . -type f -name "*.yml" -exec sed -i '' '1s/^/# SPDX-License-Identifier\: Apache-2.0\n/' {} +

I excluded files in .github/, workflows/ and .meta/ directory, plus I ignored .yamllint.yml and requirements.yml

[Wabri]

the two force pushed have been used to move from the base main branch to dev

[berndfinger]

LGTM