Support load snapshot

[zhiyuanliang-ms]

New API:

const config = await load(connectionString, {
    selectors: [
        { snapshotName: "MySnapshot" }, // load keyvalue from snapshot
        { keyFilter: "test*", labelFilter: "test" }
    ],
    featureFlagOptions: {
        enabled: true,
        selectors: [
            { snapshotName: "MySnapshot" }, // load feature flags from snapshot
            { keyFilter: "*", labelFilter: "test" }
        ]
    }
})

Allow to use snapshot selector to load key value or feature flags

Note, for expilicity, if a snapshot contains feature flag, the feature flags will only be loaded when the snapshot is used for featureFlagOptions.selectors

This implementation is the same as kubernetes provider ref and ref

Copilot reviewed 3 out of 3 changed files in this pull request and generated no comments.

Comments suppressed due to low confidence (1)

src/AzureAppConfigurationImpl.ts:946

• Ensure that the logic for handling snapshot selectors, including the error conditions, is covered by tests.

if (selector.snapshotName) {