As a user, I can define Test Run custom fields at project level

As a user, I can define Test Run "custom fields" at project level, so that users can define their values during the execution of each individual Test Run.

ACs:

• it should be possilbe to create, in the project settings, Test Run custom field types of string, number, decimal, date, boolean, multiselect, singleselect
• it should be possilbe to define a Test Run custom field as mandatory or not
• it should be possible to define default values for the Test Run custom fields (useful?)