Support starting the Azure emulator

[carole-lavillonniere]

Motivation

Minimal implementation so that LocalStack Azure emulator (localstack/localstack-azure-alpha) can be launched.

Changes

• Register the Azure emulator in internal/config: knownImages (localstack/localstack-azure-alpha), emulatorHealthPaths, and ContainerPort — so Image()/ProductName()/HealthPath()/ContainerPort() resolve for Azure.
• Add Azure to SelectableEmulatorTypes so it appears in the first-run emulator picker. Replaced the first-character SelectionKey() with an explicit unique-key map (a/s/z) — aws and azure both start with "a", so without this, selecting Azure resolved to AWS.
• Skip lstk's pre-flight platform license check for Azure, mirroring Snowflake. Introduced EmulatorType.SelfValidatesLicense() (Snowflake + Azure) and used it in start.go (pre-pull and post-pull validation) and label.go. The Azure-alpha container activates its own license against the licensing server; lstk's platform GetLicense has no catalog entry for it and would otherwise abort the start.

Tests

• Unit: Azure resolves through the start-path helpers, EmulatorTypeForImage for the Azure image, and SelfValidatesLicense truth table. Updated existing FindRunningByImage expectations to include the new repo.
• Integration: TestStartCommandSucceedsForAzure (mirrors the Snowflake start test) launches the Azure emulator and checks the container is running on the localstack-azure-alpha image and serves /_localstack/health. TestFirstRunCanSelectAzureEmulator (PTY, no Docker) confirms Azure is selectable and writes type = "azure".

1. Select

2. Started

3. Status

4. Stop

TODO before merging

• Change the image name to localstack-azure, see SMF-642

Towards FLC-679