Rename a few fields under `Domain requests` in /admin

[brooksr4]

Story

As a CISA Analyst I want to see labels that I recognize in the Domain Application List so that I can make sure that I am selecting, sorting and filtering the correct things

Acceptance Criteria

Given that I am an analyst who is beginning to review domain applications When I click the Domain Applications option on the home screen Then I am presented with a list of domain applications with the following table headers:

• Requested Domain
• Status
• Organization Type
• Submitted Date
• Requestor
• Analyst

Additional Context

This is a change to both the label and the name in the database for the following fields:

• Created At → Submitted Date
• Submitter → Requestor
• Investigator → Analyst

Issue Links

• related to: #1277

[katypies]

@h-m-f-t - I think we've already addressed some of these (ie, Analyst instead of Investigator?), and/or are aiming to address it in new tickets/issues. Should we keep this one open?

[h-m-f-t]

Actually, I think several of these are undone and still worth doing.