Add copy site to site context menu

[sejas]

Related issues

• Fixes Feature Request: Add action to duplicate a site #41 | STU-7

Proposed Changes

This PR was an iteration over #2107 created by @ndiego.

• Add Copy site… to site context menu, and in settings menu. Useful feature to quickly duplicate an entire site.
• Simplify the logic to generate names.
• It doesn't duplicate custom domain options.

Testing Instructions

• Run npm start to launch the app
• Right-click on an existing site in the sidebar
• Click "Copy site…"
• Observe the site is created and it shows a progress
• Confirm you can start the site correctly

copy-site.mp4

Pre-merge Checklist

• Have you checked for TypeScript, React or other console errors?

[wojtekn]

We could auto-start such a site to make it consistent with the 'Add site' flow and generate a thumbnail. What do you think?

[wpmobilebot]

📊 Performance Test Results

Comparing 8d5fee0 vs trunk

site-editor

Metric	trunk	8d5fee0	Diff	Change
load	2713.00 ms	2723.00 ms	+10.00 ms	🔴 0.4%

site-startup

Metric	trunk	8d5fee0	Diff	Change
siteCreation	7089.00 ms	7089.00 ms	0.00 ms	⚪ 0.0%
siteStartup	3929.00 ms	3928.00 ms	-1.00 ms	🟢 -0.0%

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Results are median values from multiple test runs.

Legend: 🟢 Improvement (faster) | 🔴 Regression (slower) | ⚪ No change

[sejas]

@wojtekn , now the site starts and generates the thumbnail as expected.
I didn't implement the custom domain, and SSL configuration, as it might require manual steps. The user can configure those form the Site settings tab.

[wojtekn]

Works great.