Adds swift and file support for `redfish` management interface
`firmware_update` step.
Adds `source` to step and `[redfish]firmware_source` to config
for setting up if and how files are staged. Support `http`, `local`
and `swift` for staging.
Adds `checksum` to step for checksum verification when file is
staged.
Story: 2008723
Task: 42067
Change-Id: Ibcc7815b32344d67f912d7dcda7283bac3582316
960f10a902