NGF: User guide for session persistence

[salonichf5]

Proposed changes

• Includes a user guide for session persistence
• updated upstream settings policy document
• updates gateway compatibility document
• updates nginx plus features list

Checklist

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• I read the Contributing guidelines
• My branch adheres to the Git conventions
• My content changes adhere to the F5 NGINX Documentation style guide
• If my changes involve potentially sensitive information¹, I have assessed the possible impact
• I have waited to ensure my changes pass tests, and addressed any discovered issues

Footnotes

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[Copilot]

Pull request overview

This PR adds comprehensive documentation for session persistence in NGINX Gateway Fabric, including a new user guide and updates to existing documentation. It explains both NGINX OSS session affinity using ip_hash and NGINX Plus cookie-based session persistence, while also documenting load balancing method configuration through the UpstreamSettingsPolicy resource.

• Adds a new session persistence user guide with practical examples for NGINX OSS and NGINX Plus
• Updates UpstreamSettingsPolicy documentation to include load balancing method configuration
• Updates API reference to reflect new fields and removed obsolete sections
• Updates Gateway API compatibility and NGINX Plus features documentation

Reviewed changes

Copilot reviewed 5 out of 5 changed files in this pull request and generated no comments.

Show a summary per file

File	Description
content/ngf/traffic-management/upstream-settings.md	Added documentation for configuring load balancing methods via UpstreamSettingsPolicy with examples for random two least_time=header and hash consistent methods
content/ngf/traffic-management/session-persistence.md	New comprehensive guide covering session persistence configuration for both NGINX OSS (ip_hash) and NGINX Plus (cookie-based), with working examples
content/ngf/reference/api.md	Updated API reference to include new load balancing fields, removed ObservabilityPolicy section, and updated Gateway API version references from v1alpha2 to v1
content/ngf/overview/nginx-plus.md	Added session persistence and advanced load balancing methods to the list of NGINX Plus features
content/ngf/overview/gateway-api-compatibility.md	Updated to reflect that sessionPersistence is now supported for HTTPRoute and GRPCRoute

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[ADubhlaoich]

Generally LGTM.

Regarding the OSS/Plus split, this document is small enough that separately documenting the different methods on one page is permissible.

If further delineation is necessary due to increasingly divergent instructions as a result of use cases, I can refactor the structure then.

Aside from everything else, you don't need to fork for the docs repo: cutting a branch directly will give you the preview links, which are easier to review.

[bjee19]

nice work! just a couple of comments.

[bjee19]

LGTM, thanks for making the change!