[agl-shell-activator] Decouple due to dependency on grpc

[agl-shell-activator] Decouple due to dependency on grpc

We also need to deal with DEPENDS and agl-shell-activator. The latter
is a pure grpc implementation, thus move it to a dynamic layer.

Bug-AGL: SPEC-4707

Change-Id: I308104b59333f69dfe416bd3721b11fb7e1b96c4
Signed-off-by: Jan-Simon Moeller <jsmoeller@linuxfoundation.org>
Reviewed-on: https://gerrit.automotivelinux.org/gerrit/c/AGL/meta-agl/+/28513
Reviewed-by: Denys Dmytriyenko <denys@konsulko.com>
Reviewed-by: Marius Vlad <marius.vlad@collabora.com>
Tested-by: Jenkins Job builder account
ci-image-build: Jenkins Job builder account
ci-image-boot-test: Jenkins Job builder account