Rebase and Merge with One Click settings migration

• Add a database migration on the projects table to add an additional column rebase_and_merge_with_one_click.
• Enforce validation on rebase_and_merge_with_one_click so it can only be true when Merge commit with semi-linear history or fast-forward merge methods are selected.
• This column should default to true if the above condition is met, and be not NULL.
• This validation should also be duplicated on the Project model.