Docs: Improve AWS PrivateLink documentation for GitLab Dedicated
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## Problem to solve
**Primary issue:** Add conceptual overview to the [AWS Private Link connectivity](https://docs.gitlab.com/administration/dedicated/configure_instance/network_security/#aws-private-link-connectivity) section and improve overall information architecture for both inbound and outbound Private Link documentation.
**Specific needs:**
1. The H2 section currently has no content. It should include:
- Overview of what AWS PrivateLink connectivity provides
- Explanation of inbound vs outbound connection types
- Common constraints (regional limitations, etc.)
- Link to AWS documentation
2. Move troubleshooting sections to the end of the overall section instead of after individual topics.
**Secondary issue:** Terminology inconsistency throughout Private Link documentation:
- "Inbound Private Link" (GitLab's feature name)
- "PrivateLink" (AWS service name)
- "Privatelink" (inconsistent capitalization)
**Impact:**
- Users lack context before diving into specific procedures
- Mixed terminology confuses users about whether we're referring to GitLab's implementation or AWS technology
- Information architecture doesn't follow GitLab's topic type guidelines
**Proposed solutions:**
1. **Add conceptual content:** Put user benefits first and treat AWS PrivateLink as the underlying technology
2. **Standardize terminology:** Either stick with AWS terminology ("PrivateLink") or define GitLab-specific terminology ("private inbound connections") with clear AWS context
3. **Restructure content:** Align with [topic types](https://docs.gitlab.com/development/documentation/topic_types/) and provide better context before specific procedures
This puts the user benefit first, provides better context, and creates consistency across all GitLab Dedicated networking documentation.
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