docs(changelog): changelog for lts-v2.8.15 release

Generated with the command:
npm run release -- --release-as 2.8.15

Signed-off-by: Yann Gautier <yann.gautier@st.com>
Change-Id: Ibb920e90a6f44a858b9f4709dbeb22e22ab86e78
7 files changed