Add the MAINTENANCE_BANNER_TEXT variable to generic_env_config
Add the MAINTENANCE_BANNER_TEXT variable to generic_env_config

gsehub/configuration,hks-epod/configuration,edx/configuration,Stanford-Online/configuration,rue89-tech/configuration,appsembler/configuration,stvstnfrd/configuration,EDUlib/configuration,gsehub/configuration,stvstnfrd/configuration,stvstnfrd/configuration,rue89-tech/configuration,stvstnfrd/configuration,EDUlib/configuration,mitodl/configuration,edx/configuration,Stanford-Online/configuration,Stanford-Online/configuration,rue89-tech/configuration,gsehub/configuration,mitodl/configuration,rue89-tech/configuration,hks-epod/configuration,EDUlib/configuration,Stanford-Online/configuration,stvstnfrd/configuration,arbrandes/edx-configuration,EDUlib/configuration,arbrandes/edx-configuration,appsembler/configuration,edx/configuration,arbrandes/edx-configuration,gsehub/configuration,hks-epod/configuration,edx/configuration,arbrandes/edx-configuration,Stanford-Online/configuration,hks-epod/configuration,mitodl/configuration,gsehub/configuration,appsembler/configuration,EDUlib/configuration,rue89-tech/configuration,arbrandes/edx-configuration,appsembler/configuration,hks-epod/configuration,mitodl/configuration