Consider a slug for dashboard views instead of an index in the view query param

Context

Follow-up from !247361 (comment 3621858644)

!247361 (merged) added deep linking to a specific view of a multi-view analytics dashboard using a ?view=<index> query param. The index was chosen because it requires no extra configuration when setting up a dashboard, and titles are not guaranteed to be URL-safe or unique.

As raised in review, the positional index has a drawback: if views are reordered, existing bookmarks become stale and point at the wrong view.

Proposal

Discuss adding a slug property to DashboardView in the analytics_dashboard.json schema and using it in the query param instead of the index, e.g. ?view=deployment-frequency.

Trade-offs surfaced so far:

• Pro: bookmarks survive view reordering, and the URL becomes human readable.
• Pro: a slug can be renamed independently of the view title, so it can stay stable across title changes.
• Con: bookmarks still break if the slug itself changes, so this moves the bookmark dependency from reordering to renaming rather than removing it.
• Con: more configuration required when defining a dashboard.

Notes

• The work already done in !247361 (merged) supports the slug approach, so this is an additive change.
• This should be decided before the explore_analytics_dashboards feature flag is rolled out, while the URL format is not yet relied upon by users.

Proposal for resolution

1. Agree on whether to move from index to slug.
2. If yes: add slug to the DashboardView schema, decide whether it is required or optional (with a fallback to index), and update the deep linking to read/write slugs.