On Monday, a billboard calling for James Gunn to be rehired as director of “Guardians of the Galaxy Vol. 3” went up just four miles away from Disneyland. The ad was paid for by a fan-created crowdfunding campaign that has raised just under $5,000 since September. Reading “Save the Galaxy: James Gunn for Vol. 3,” the digital sign, which went up Monday in in Garden Grove, California, directs people to the campaign’s website, www.rehirejamesgunn.com.