Avoid using common names in a module which will be included to the Resource::Context

The following discussion from !2404 (merged) should be addressed:

• @godfat-gitlab started a discussion:

  We're including this to a almost global context: plugins/growth_refine_automation_helper.rb

  This means we should use more unique method names, otherwise it's easy to conflict with others. What do you think about maybe call this gitlab_com_api_token_header?

  This actually applies to all the methods in this module, not just this one. Even constants. COMMENT_HEADING is probably too generic, too. If we want to use generic names, we should not include them to a almost global context.

  I don't see we're using token_header elsewhere, yet, and I want to get tests fixed first, so I am taking the fix as-is, thank you!