Fix #8493: Add IgnoredPurgeIndexes configuration for AWS OpenSearch

[Obine-adjada]

• Document how to handle protected system indexes
• Add IgnoredPurgeIndexes parameter configuration
• Explain why this setting is required to avoid purge errors
• Provide command to identify protected indexes

Fixes #8493

Summary

Ticket Link

[mattermost-build]

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[cwarnermm]

Thank you, @Audrey-andy! Are you open to signing the Mattermost CLA? This step is required to incorporate your PR updates into our documentation codebase.

[Obine-adjada]

/check-cla

[mattermost-build]

This PR has been automatically labelled "stale" because it hasn't had recent activity.
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[cpoile]

@carlisgg I'm assigning you because you've looked at elastic search recently, correct? If you're not comfortable let me know and I'll find another reviewer, thanks!

[cwarnermm]

Friendly reminder to sign the Mattermost CLA, @Obine-adjada.

[cwarnermm]

@Obine-adjada - We can't move forward with your docs PR without a signed CLA. Closing.