[Lens] Saved object should register reference to index patterns to keep exports/imports consistent

[wylieconlon]

Related issues:

• Handling saved object references in expressions #59960

This has the following parts:

• Extend getPersistableState to return saved objects references as well. The persistable state object shouldn't include any actual saved object ids, only the names referenced in the reference array. E.g. getPersistableState(state: T) => { persistableState: T2, references: SavedObjectReference[]}
• Extend initialize by taking that reference array to put the actual saved object ids back into the state. e.g. initialize(persistedState: T2, references: SavedObjectReference[]) => Promise<T>
• Do the same thing for the frame level state (filters). Might be possible to reuse some logic from the data plugin, but not necessarily
• Concatenate all saved object reference arrays before saving the saved object
• Do not save the expression in the saved object. Instead refactor the embeddable to initialize the right visualization and data source based on the state and call toExpression on them to get the expression. x-pack/plugins/lens/public/editor_frame_service/editor_frame/expression_helpers.ts contains helpers to piece together the expression
• Add a migration to remove the expression from all saved objects
• Add a migration to pull out saved object references from existing saved objects (basically run the getPersistableState function)

[elasticmachine]

Pinging @elastic/kibana-app (Team:KibanaApp)

[wylieconlon]

@timroes I don't have a clear idea of the implications of this change on our saved object format. It seems like we will need to write some logic that keeps references and our app state consistent.

[timroes]

The final implementation of this service outlined in (#59960) will be part of the persistable state service (#62950) - also see Expression Roadmap (#46909). Since this implementation will still take some time, we've decided to provide a minimal simplified inject/extract inside Lens, that will extract references from the esaggs and the kibana_context (inside filters) function. This functions should ideally follow the API outlined in #59960 so we can later simply replace them by the real API once ready.

[timroes]

The related PR: #72438