fix default outbound annotation

[kon-angelo]

How to categorize this PR?

/area control-plane
/kind bugfix
/platform azure

What this PR does / why we need it:

Which issue(s) this PR fixes:
Fixes #

Special notes for your reviewer:

Release note:

Fix a bug that disabled subnet's default outbound access.

[gardener-robot]

@kon-angelo Label kind/bugfix does not exist.

[hebelsan]

/lgtm

needs change

[github-actions]

This change refactors and fixes how default outbound access for subnets is configured. It renames an internal field to better align with the Azure API and inverts the associated logic. More importantly, it corrects a bug where the configuration annotation was being read from the wrong resource. This ensures the disable-default-outbound-access shoot annotation is correctly applied, allowing users to control this networking behavior as intended.

Walkthrough

• Bug Fix: Corrected the handling of the disable-default-outbound-access annotation. The controller now properly reads this annotation from the Shoot specification, allowing users to successfully disable default outbound internet access for newly created subnets.
• Refactor: Renamed internal fields and functions related to subnet outbound access to improve code clarity and align more closely with the underlying Azure API's DefaultOutboundAccess property.

_{Model: gemini-2.5-pro | Prompt Tokens: 961 | Completion Tokens: 174}

[hebelsan]

/lgtm