Set a max length on the deploykeys.ssh_search_key field
    
    MySQL refuses to create an index over a column with an unlimited length.
    Since we always use SHA256, we know it's always of style
    "SHA256:jIHuaHxaQhx0y3folM5eHR+Ktr5D9fLaS97DB7nkvnk",
    With exact length 50.
    
    Signed-off-by: Patrick Uiterwijk <patrick@puiterwijk.org>