SQL Server : which role grants permission to execute all stored procedures?
If you are using schemas other than the default dbo schema, create a database role per schema and grant EXECUTE on the schema to the role.

e.g.
For the default dbo schema:

CREATE ROLE role_exec_dbo
GO
GRANT EXECUTE ON SCHEMA::dbo to role_exec_dbo
GO


For a new schema:

CREATE SCHEMA mySchema
GO
CREATE ROLE role_exec_mySchema
GO
GRANT EXECUTE ON SCHEMA::mySchema to role_exec_mySchema
GO