chore: bump egress-gateway to v0.1.2

[rowan-stein]

User request

Consume the released egress-gateway data-plane runtime so full-apply and e2e can validate real secret injection through the gateway.

Specification

agynio/egress-gateway PR #8 is merged and released as v0.1.2; image and chart release succeeded.

Update bootstrap according to existing public GHCR OCI patterns:

• Bump stacks/platform/variables.tf egress_gateway_chart_version default from 0.1.1 to 0.1.2.
• The default image tag should continue to derive from the chart version unless explicitly overridden.
• Do not add GHCR credentials, imagePullSecrets, repository credentials, or token-based special cases.
• Run the standard bootstrap validation.
• Open one PR linked to this issue.

Acceptance criteria

• Bootstrap deploys egress-gateway chart/image 0.1.2.
• Existing public GHCR OCI chart/image patterns remain unchanged.
• CI/full-apply passes.