[v10.1.x] Alerting: Make shareable alert rule link work if rule name contains forward slashes

[grafana-delivery-bot]

Backport aaaef71 from #75362

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URL produced by "Copy link to rule" button would not open the rule page on Grafana Cloud instances if alert name contains forward slashes. This is because proxy in front of grafana auto unescapes slashes thereby mangling the URL.

This is solved by using unescapePathSeparators and escapePathSeparators which are intended to solve this exact problem and are used for rule id, but were not being used for the short link.

Fixes #74807

Special notes for your reviewer:

Please check that:

• It works as expected from a user's perspective.
• If this is a pre-GA feature, it is behind a feature toggle.
• The docs are updated, and if this is a notable improvement, it's added to our What's New doc.