Restrict merges to specific source branches

G'day team,

We have had a customer raise a request that they would like to see implemented.
Essentially, our branch restrictions only allow restricting certain users to be able to perform merges, however these users can merge any source branch into the destination branch.
They would like to see the option to allow only certain source branches to be able to be merged into destination branches.

For example, they would only like to allow dev branch to be merged into master, restricting all other branches from being able to be merged into master.
This could be extended to include prefixes as well, for example: only "release/*" can ever be merged into the master branch.

Thanks,
Ben