[8.18] [DOCS] MITRE ATT&CK® v17.1 being mapped to 8.18.7 and 8.19.4 (backport #7061)

[mergify]

Contributes to elastic/docs-content#2791. Updates the note that communicates the mapping between Security and MITRE ATT&CK®.

Corresponding 9.x updates: elastic/docs-content#2898

Preview

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This is an automatic backport of pull request #7061 done by Mergify.

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