This commit reduces the interface to Load() a bit, in preparation for
unexporting NewBuilder and having everything call Load.
The three arguments are reduced to a single argument by moving the other
two into the options struct.
The three return values are reduced to two by moving the RuntimeConfig
and Warnings into a LoadResult struct.
All commands which read config (agent, services, and validate) will now
print warnings when one of the config files is skipped because it did
not match an expected format.
Also ensures that config validate prints all warnings.
The nil value was never used. We can avoid a bunch of complications by
making the field a string value instead of a pointer.
This change is in preparation for fixing a silent config failure.
Flags is an overloaded term in this context. It generally is used to
refer to command line flags. This struct, however, is a data object
used as input to the construction.
It happens to be partially populated by command line flags, but
otherwise has very little to do with them.
Renaming this struct should make the actual responsibility of this struct
more obvious, and remove the possibility that it is confused with
command line flags.
This change is in preparation for adding additional fields to
BuilderOpts.
