Use "created" in epics and MRs

What does this MR do?

Related: #246959 (closed)

I'll see what else I can find.

Screenshots

Epic header

Test URL: http://127.0.0.1:3001/groups/flightjs/-/epics/5

Before	After

Epic - nested epics/issues

Test URL: http://127.0.0.1:3001/groups/flightjs/-/epics/5 (+ add subepic and reopen attached issue)

Before	After

Epic swimlanes in issue board

Test URL: http://127.0.0.1:3001/groups/flightjs/-/boards?group_by=epic (+ add a start/due date to one of the epics)

Before	After

Epic list

Test URL: http://127.0.0.1:3001/groups/flightjs/-/epics

Before	After

Merge request list

Test URL: http://127.0.0.1:3001/flightjs/Flight/-/merge_requests

Before	After

Merge request dashboard

Test URL: http://127.0.0.1:3001/dashboard/merge_requests?assignee_username=root

Before	After

Global search (issues/MRs)

Test URL: http://127.0.0.1:3001/search?group_id=26&project_id=6&repository_ref=&scope=issues&search=lorem&snippets=false

Before	After

Global search (epics)

Test URL: http://127.0.0.1:3001/search?group_id=26&project_id=&repository_ref=&scope=epics&search=lorem&snippets=false

Before	After

Related issues widget

Test URL: http://127.0.0.1:3001/flightjs/Flight/-/issues/6 (+ add a related issue)

Before	After

"Currently opened" tooltips

Test URLs:

• Issues: http://127.0.0.1:3001/flightjs/Flight/-/issues
• MRs: http://127.0.0.1:3001/dashboard/merge_requests?assignee_username=root
• Epics: http://127.0.0.1:3001/groups/flightjs/-/epics
• Test cases: http://127.0.0.1:3001/flightjs/Flight/-/quality/test_cases

Item	Before	After
Issues
MRs
Epics
Test cases

Does this MR meet the acceptance criteria?

Conformity

• 📋 Does this MR need a changelog?
  • I have included a changelog entry.
  • I have not included a changelog entry because _____.
• Documentation (if required)
• Code review guidelines
• Merge request performance guidelines
• Style guides
• Database guides
• Separation of EE specific content

Availability and Testing

• Review and add/update tests for this feature/bug. Consider all test levels. See the Test Planning Process.
• Tested in all supported browsers
• Informed Infrastructure department of a default or new setting change, if applicable per definition of done

Security

If this MR contains changes to processing or storing of credentials or tokens, authorization and authentication methods and other items described in the security review guidelines:

• Label as security and @ mention @gitlab-com/gl-security/appsec
• The MR includes necessary changes to maintain consistency between UI, API, email, or other methods
• Security reports checked/validated by a reviewer from the AppSec team