Handle empty state when grouping by ARM tag

[Copilot]

When selecting "Group by ARM Tag..." with no tags in the subscription, users see an empty input box with only a placeholder—no indication that tags need to be created first.

Changes

• Check for empty tags in getQuickPicks: Throw NoResourceFoundError with actionable message when no tag keys exist
• Error message: "No tag keys found. Please add tags to your resources to use this grouping option."

async function getQuickPicks(context: IActionContext, subscription: AzureSubscription): Promise<QuickPickItem[]> {
    const client = await createResourceClient([context, createSubscriptionContext(subscription)]);
    const tags = await uiUtils.listAllIterator(client.tagsOperations.list());
    
    if (tags.length === 0) {
        (context as { noItemFoundErrorMessage?: string }).noItemFoundErrorMessage = localize('noTagKeysFound', 'No tag keys found. Please add tags to your resources to use this grouping option.');
        throw new NoResourceFoundError(context);
    }
    
    return tags.map(tag => ({
        label: nonNullProp(tag, 'tagName'),
    }));
}

Follows the same pattern as deleteResourceGroupV2.ts for empty resource lists.

Warning

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Original prompt

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This section details on the original issue you should resolve

<issue_title>“Group by ARM Tag...” shows an empty input box with no guidance when no tags exist</issue_title>
<issue_description>OS: Win11
Build Version: 20251210.1

Repro Steps:

1. Ensure that none of the resources/resource groups in the current subscription have any ARM tags.
2. Open the Azure Resources view -> Click "Group By" icon -> Select “Group by ARM Tag...”.
3. Observe the UI for selecting the tag key.

Expect:
There is a clear empty-state message, such as “No tag keys found. Please add tags to your resources to use this grouping option.”

Actual:
The UI displays an empty input box with placeholder “Select the tag key to group by…”.
</issue_description>

Comments on the Issue (you are @copilot in this section)

• Fixes “Group by ARM Tag...” shows an empty input box with no guidance when no tags exist #1324

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