[DOCS] Viewer role needs experimental settings for Fleet UI access

[geekpete]

Make users aware that for 8.17, viewer role requires Fleet experimental settings enabled for read only access to the Fleet UI.
Used a hard link to Kibana 8.17 docs.
This mention isn't required for 8.18 as the Fleet experimental setting is enabled by default.
I wasn't able to locate the setting in 9.x docs, so may not be relevant to that version.

[github-actions]

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[elasticsearchmachine]

@geekpete please enable the option "Allow edits and access to secrets by maintainers" on your PR. For more information, see the documentation.

[elasticsearchmachine]

Pinging @elastic/es-docs (Team:Docs)

[shainaraskas]

thanks, @geekpete! I left a quick question on here based on my read of the setting

I wasn't able to locate the setting in 9.x docs, so may not be relevant to that version.

both of these pages / settings are available in the new docs:

https://www.elastic.co/docs/reference/kibana/configuration-reference/fleet-settings#_preconfiguration_settings_for_advanced_use_cases
https://www.elastic.co/docs/deploy-manage/users-roles/cluster-or-deployment-auth/built-in-roles

I assume that if experimental features (or this experimental feature) are enabled by default in 8.18, the same would go for 9.0+.

[geekpete]

I had also confirmed with the Kibana team that per the 8.17 docs mention, the read-only Fleet access is unsupported and only becomes supported in 8.18 and later where it's on by default.

If we're showing users how to enable this in 8.17 then we should probably also explicitly warn them that doing so is unsupported and also generally that experimental features should not be enabled in production environments.

We also have an updated KB article to explain why read-only Fleet access might show errors in 8.17 due to not being enabled, and also warn and explain the different behaviour in the versions and directs users to upgrade to a version where the functionality is enabled by default and supported.
https://support.elastic.co/knowledge/6225856d

Since enabling the experimental feature is both unsupported and not recommended in production, I'm leaning more towards just closing this PR since the newer versions avoid the issue by having the functionality on by default.

[elasticsearchmachine]

Pinging @elastic/core-docs (Team:Docs)

[geekpete]

Closing since this all became on by default in newer versions and in the previous versions it wasn't supported, just possible. We also have the public knowledge article to explain for anyone hitting the issue https://support.elastic.co/knowledge/6225856d.