"condor_config_val" equivalent CLI tool for Pelican

[bbockelm]

Currently, there's no simple way to dump or share the Pelican configuration. We should add a new sub-command to Pelican, pelican config, with the following functionality:

• pelican config dump: dump the entire current configuration. Defaults to yaml output but, based on CLI flags, can output to JSON.
• pelican config inputs: Prints out the configuration file(s) used as inputs to the configuration.
• pelican config get <name1> <name2> ... <nameN>: Prints out all configuration variables and the values matching name1, name2, .... The matching rules should be based on Unix (case-insensitive) globs on any part of the string. So, pelican config get log would match any config value with log in the name. For config entries that are lists or non-trivial structures, the printed value should be JSON-encoded and single-line.
• pelican config summary (pelican config, with no sub-command, defaults to summary): Prints, in the specified format, settings that differ from the default configuration.

[jhiemstrawisc]

This appears to be a repeat of issue #1125, but this issue provides more detail about the expected interface. I'll close the other.

[bbockelm]

Additional items / discussion:

• config get should match both substring and globs. So, config get origin would match Logging.Origin.Http even though, if it was glob-only, it wouldn't match.
• Have a flag (--component?) that allows one to narrow-down the relevant config items.
• Have a flag (--show-deprecated?) that allows one to show deprecated configuration value; otherwise, do not show them.
• Make sure to sort the resulting output. Similarly for --show-hidden.

Things that would be nice to have -- but could possibly be done as a follow-up:

• A flag to print out the documentation itself.
• A flag to show only non-default values. Realistically, this would require us to programmatically generate the defaults from the parameters.yaml instead of hardcoding them in a resource.