Missing PRIMERO_MESSAGE_SECRET in local.env.sample.development

[merlos]

PRIMERO_MESSAGE_SECRET is not set in local.env.sample.development file.

Steps to reproduce

cd docker 
cp local.env.sample.development local.env
./build.sh all
./compose.local.sh up

Application does not run because in the script check_required_variables function of the entrypoint.sh of the docker/application/root this variable is required.

Proposed solution:

Add PRIMERO_MESSAGE_SECRET to the example file.