Filter option in custom format. Default value is empty or "any".
Available formats:
* any pull requests applied for this project: "any", "*" or empty string.
* filtered by destination branch: "my-branch" or more complex reg-ex filter "r:^master" (must be started with "r:" and case insensitive match).
* filtered by source and destination branches: "s:source-branch d:dest-branch"
* filtered by source and destination branches with regex: "s:r:^feature d:r:master$"
* filtered by many destination/source branches: "s:one s:two s:three d:master d:r:master$"
* filtered by many sources branches: "s:one s:two s:r:^three d:"
When you using format with source branch filter "s" or destination filter "d", you must cpecify great than one source and destination filter, eg "s:1 s:2 s:... d:".
Any sources and any destinations for pull request:
* filter string: "*"
* filter string: "s: d:"