[CI] Drop temp site-copy code and more

[chalin]

• Contributes to Finalize monorepo setup #2436
• Drops temporary site-copy code
• Adds htmltest URL ignore rule for deploy-preview URLs, b/c link checking is done before the preview is served

[chalin]

The ignore rule resolved the deploy-preview link-checking errors, see https://app.netlify.com/projects/docsydocs/deploys/6969622d9089a90008acbdc2:

4:55:19 PM: htmltest started at 09:55:19 on public
4:55:19 PM: ========================================================================
4:55:19 PM: running in concurrent mode, this is experimental
4:55:19 PM: ✔✔✔ passed in 314.826616ms
4:55:19 PM: tested 167 documents

[chalin]

Successful build: https://app.netlify.com/projects/docsydocs/deploys/6969689834b8f200084575f1