Add space getting-started reference

[aws-brianxia]

What's changing and why?

Adds "Space" as a new entry in the Getting Started documentation table of contents (doc/getting_started.md). This links to the existing doc/getting_started/space.md page, making the Space getting-started guide discoverable from the top-level getting started navigation alongside Cluster Management, Training, and Inference.

Before/After UX

Before:

The Getting Started toctree only listed three sections:

• Cluster Management
• Training
• Inference

Users had no way to navigate to the Space getting-started guide from the main Getting Started page.

After:

The Getting Started toctree now includes four sections:

• Cluster Management
• Training
• Inference
• Space

Users can navigate directly to the Space getting-started guide from the Getting Started page.

How was this change tested?

This is a documentation-only change (adding a toctree entry). Verified that the target file doc/getting_started/space.md exists.

Are unit tests added?

No — documentation-only change, no unit tests needed.

Are integration tests added?

No — documentation-only change, no integration tests needed.

Reviewer Guidelines

‼️ Merge Requirements: PRs with failing integration tests cannot be merged without justification.

One of the following must be true:

• Changes are documentation-only