Tie Logging.Level to default log levels in Xrootd

[jhiemstrawisc]

Right now we can set logging levels in the Pelican process with:

Logging:
  Level: <level>

where valid levels are Trace, Debug, Info, Warn, Error, Fatal, and Panic.

We can also set logging levels in the XRootD process with:

Logging:
  Origin:
    <component>: <level>
  Cache:
    <component: <level>

It sure would be swell if the value from Logging.Level could be applied as a calculated default for all the Origin/Cache components unless those components are explicitly set otherwise.