Make copy for entering URLs consistent for work items

Description

Make copy for entering URLs consistent for work items:

• Fields where you can enter an item's URL should use the phrase: Enter <item> URL instead of Paste <item> link to follow:
  • Style guidance for enter: https://docs.gitlab.com/ee/development/documentation/styleguide/word_list.html#enter
  • Our own terminology: we use "link" in "linked items", so URL is more precise.
• Where the placeholder text refers to #123 and !123, these should be called <#issue ID> and <!merge request ID>, and so on, with ID capitalized.

Related items

• This thread: #427975[Create_add_workflows.png] (comment 1920852406)
• Make copy for entering URLs consistent for issu... (!154149 - merged)

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The following discussion from !154149 (merged) should be addressed:

• @ameliabauerly started a discussion: (+5 comments)

  Hey @msedlakjakubowski! I just looked at the changes on issues, incidents and epics, and all seem as expected. It looks like the changes might still need to be made on the "linked items" widgets in tasks and OKRs though, or maybe there's a reason you didn't update those instances? They seem to be using the old "paste" text:

  OKR	Tasks

  On a related note, I spotted that you decided not to update the text on the child widget on issues/incidents, but you did update the text on the epic child widget. I wonder if it's worth also updating the language on the issue/incident child widgets, too, so it aligns with the new language elsewhere? Even updating "paste" to "enter"? Or maybe there's a reason you decided not to make that change at this point?

  I guess I'm just wanting to clarify why some instances were updated but not others. I'm guessing there's a good reason for this but, I wasn't sure so, wanted to at least check in!