Fix Health Client Formatting

[rob05c]

Fixes Health Client formatting and Go idioms, primarily GoDoc comments and naming conventions.

Which Traffic Control components are affected by this PR?

• Traffic Control Health Client (tc-health-client)

What is the best way to verify this PR?

Run Health Client, verify behavior is unchanged.

If this is a bugfix, which Traffic Control versions contained the bug?

Not a bug fix

PR submission checklist

• ~[x] This PR has tests~ no code behavior change, existing behavior is covered by tests
• ~[x] This PR has documentation~ no docs, no interface change
• ~[x] This PR has a CHANGELOG.md entry~ No changelog, no interface change
• [x] This PR DOES NOT FIX A SERIOUS SECURITY VULNERABILITY (see the Apache Software Foundation's security guidelines for details)