[avatar_experimental] - Copy avatar from external

Copy avatar from external into pandora and mark it
as experimental and link it with the interfaces in
pandora_experimental.
At some point avatar will be only in external/ but
currently it is easier to iterate on it and more
flexible in avatar_experimental.

Bug: 245749560
Test: atest-dev avatar -v
Change-Id: I79a2ac247dc37becc61e2fc2158f5836f1894cfe