dashapi: add query mocking functionality
dashapi: add query mocking functionality

At the moment it's only possible to do by emulating http requests, which
looks like an overkill for simple query mocking in unit tests.

google/syzkaller,google/syzkaller,xairy/syzkaller,xairy/syzkaller,xairy/syzkaller,google/syzkaller,xairy/syzkaller,google/syzkaller,google/syzkaller,xairy/syzkaller,xairy/syzkaller,google/syzkaller,google/syzkaller,xairy/syzkaller