* Show error in logs if passing invalid flags in yaml
The YAML configs pass if an invalid flag is set, this causes frustration
because the flag could have been mispelled causing a huge mystery.
This will strictly check if the flags are deserialized, if a flag
doesn't exist, it will error out as a Fatal error with appropriate
reasoning which flag is wrong.
* Fix review comments to make some of them non-fatal
* Make yaml.TypeError a pointer
* Remove UnmarshalStrict from spectests since they use a different YAML package
Co-authored-by: Preston Van Loon <preston@prysmaticlabs.com>
