[8.14] Add mTLS flags to 'Configure SSL/TLS' docs (backport #1099)

[mergify]

This updates the Configure SSL/TLS for self-managed Fleet Servers page to include the recently added mTLS flags. I also added the --fleet-server-policy=fleet-server-policy flag since it was missing, but I see it in the example from the mTLS flags PR.

Closes: #1098

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This is an automatic backport of pull request #1099 done by [Mergify](https://mergify.com).

[github-actions]

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