Lacking support for Lookup table files

[bruno-yamada-mck]

As a user of this provider, I would like to use it for creating my lookup table files and keeping it up-to-date

Related thread:

• https://community.splunk.com/t5/Splunk-Search/Can-you-create-modify-a-lookup-file-via-REST-API/m-p/193671

[akohring]

Created a PR to add support for lookup table files https://github.com/splunk/terraform-provider-splunk/pull/196