Allow multiple files to be linted on cli

[matchbookmac]

Issue #, if available:
N/A

Description of changes:
At the moment, the statelint command only lints the first file passed as an argument. For example, the following will only lint snapshot.json:

statelint snapshot.json processing.json
# 2 errors:
# State Machine.States.create_partition.Resource is "${partition_lambda}" but should be A URI
# State Machine.States.import.Resource is "${import_lambda}" but should be A URI

This update will lint all files passed to the command and output the results, or exit if there are no issues found:

statelint snapshot.json processing.json
# 2 errors: for snapshot.json
#  State Machine.States.create_partition.Resource is "${partition_lambda}" but should be A URI
#  State Machine.States.import.Resource is "${import_lambda}" but should be A URI
# 9 errors: for processing.json
#  State Machine.States.header_create.Resource is "${header_create_lambda}" but should be A URI
#  State Machine.States.validation_status.Resource is "${validation_status_lambda}" but should be A URI
#  State Machine.States.invalid_wrap_up.Branches[0].States.start_crawler_failure.Resource is "${crawler_start_lambda}" but should be A URI

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[la-sanchez]

Any chance this PR could be merged?