Filter by branch on global search

Problem statement

A fairly frequent use case for global search at organizations is to find all instances of a particular usage of code, variable, secret, dockerfile, etc.

One of the use cases is to try to validate that all instances of a particular piece of code have been updated/removed/etc. For these use cases it is important to be able to filter on the default branch, so you don't get stale false positives from old branches.

Proposal

There are two potential ways to solve this:

1. Add a filter option to allow filtering on a specific branch, for example branch:master
2. Add a boolean to allow filtering on whatever the default branch is, for example default_branch:true