[7.x] [Security Solution][Detections] Fix grammatical error in validation message for threshold field in "Create new rule" -> "Define rule" (#84490)

[banderror]

Backports the following commits to 7.x:

• [Security Solution][Detections] Fix grammatical error in validation message for threshold field in "Create new rule" -> "Define rule" ([Security Solution][Detections] Fix grammatical error in validation message for threshold field in "Create new rule" -> "Define rule" #84490)

[kibanamachine]

💚 Build Succeeded

• continuous-integration/kibana-ci/pull-request
• Commit: 09eb57c

Metrics [docs]

Async chunks

Total size of all lazy-loaded chunks that will be downloaded as the user navigates the app

id	before	after	diff
securitySolution	8.0MB	8.0MB	+3.0B

To update your PR or re-run it, just comment with:
@elasticmachine merge upstream