* add hashfunc field to EntryFormatter struct and adjust NewEntryFormatter function and tests
* add HeaderAdjuster interface and require it in EntryFormatter
dquote> adjust all references to NewEntryFormatter to include a HeaderAdjuster parameter
* replace use of hash function in AuditedHeadersConfig's ApplyConfig method with Salter interface instance
* fixup! replace use of hash function in AuditedHeadersConfig's ApplyConfig method with Salter interface instance
* review feedback
* Go doc typo
* add another test function
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Co-authored-by: Peter Wilson <peter.wilson@hashicorp.com>