chore: Add `initialCheck` capability to alert/flash content API

[gethinwebster]

Description

Related links, issue #, if available: n/a

How has this been tested?

Review checklist

The following items are to be evaluated by the author(s) and the reviewer(s).

Correctness

• Changes include appropriate documentation updates.
• Changes are backward-compatible if not indicated, see CONTRIBUTING.md.
• Changes do not include unsupported browser features, see CONTRIBUTING.md.
• Changes were manually tested for accessibility, see accessibility guidelines.

Security

• If the code handles URLs: all URLs are validated through the checkSafeUrl function.

Testing

• Changes are covered with new/existing unit tests?
• Changes are covered with new/existing integration tests?

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[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Project coverage is 96.21%. Comparing base (7693793) to head (8b7a60b). Report is 11 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #2879   +/-   ##
=======================================
  Coverage   96.21%   96.21%           
=======================================
  Files         761      761           
  Lines       21490    21511   +21     
  Branches     7359     7357    -2     
=======================================
+ Hits        20676    20697   +21     
  Misses        761      761           
  Partials       53       53           

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