docs: document the Auditor role and the audit log exporter

[utkuozdemir]

Omni has a new Auditor role that grants read access plus the audit log and nothing else, so reading the audit log no longer requires Admin. Access is granted by exact role rather than by seniority, so Operator does not get it despite being more privileged, and the role cannot be assigned by an access policy or a SAML label rule.

A new page covers the audit log exporter: how to run it, where an export starts, how it resumes across restarts, and what stops it rather than being retried. The existing audit log page said Omni had no built-in way to export, so it now points at the new page instead. The event reference also drops two fields that no longer exist and gains the resource id and the audit log access event type.

The agent guide is corrected while here. It described the navigation as being edited directly in the generated file rather than in the per-product configs it is built from, and it now also lists the checks CI runs so they can be run before pushing.

Draft until the Auditor role lands in Omni and ships in a release, since the docs site publishes continuously and would otherwise describe a role that cannot be selected yet.

Part of siderolabs/omni#2985.

[utkuozdemir]

@Iheanacho-ai Let's keep this not merged until we release Omni 1.10.0.

[Iheanacho-ai]

The hierachy of your doc is off. This is a better hierachy:

• Introduction
• Prerequisites
• Set up the exporter (parent for the actual procedure)
  • Step 1: Create a service account
  • Step 2: Run the exporter
• Configure behavior (parent for the tuning topics)
  • Choose where the export starts
  • Resume across restarts
• Understand the delivery guarantees
• Troubleshoot

[utkuozdemir]

The hierachy of your doc is off. This is a better hierachy:

• Introduction

• Prerequisites

• Set up the exporter (parent for the actual procedure)

  • Step 1: Create a service account
  • Step 2: Run the exporter

• Configure behavior (parent for the tuning topics)

  • Choose where the export starts
  • Resume across restarts

• Understand the delivery guarantees

• Troubleshoot

reworked as you suggested