Add limited_owner role to capabilities reference (#3243)

## Type of change
**Documentation Update**
- Added `limited_owner` as a new built-in administrative IAM role
throughout the capabilities reference
- Documented `limited_owner` capabilities: read access across all
resources, plus `identity` and `role_bindings` create permissions, and
image pull access

## What should this PR do?

resolves chainguard-dev/internal#5787

## Why are we making this change?

The `limited_owner` role exists in the Chainguard platform but was not
documented in the capabilities reference. Customers and admins need to
understand how this role differs from `owner`, `viewer`, and other
administrative roles when making IAM decisions.

## What are the acceptance criteria?

- `limited_owner` appears in the Built-in Roles Summary under
Administrative Roles, positioned between `viewer` and `console_viewer`
- `limited_owner` appears in all applicable rows of the Chainguard Role
Capabilities table, positioned after `viewer` and before
`console_viewer`
- `limited_owner` row is present in the Role Capabilities Comparison
table showing ✅ for Pull Images, List Tags/Repos, View SBOMs/Diffs,
Create IAM Resources, and Create Pull Tokens, and ✕ for Libraries Access
- The role count in the comparison section no longer references a
hardcoded number

## How should this PR be tested?

1. Check the preview link and navigate to the Built-in Roles &
Capabilities page under Administration > IAM Organizations > Roles &
Role-bindings
2. Verify `limited_owner` appears in all three places: the summary list,
the capabilities table (after `viewer` in each row), and the comparison
table

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Signed-off-by: Mark Drake <mark@chainguard.dev>

Author: SharpRake