Functional test for saved objects import/export UI

[bhavyarm]

Tests for testing export/import using saved objects UI:

For 7.x to 8.x import:

Data set:
sample dashboards and all the beats dashboards viz .ndjson

Tests:

1. To empty Kibana - import the file with related objects and make sure import works fine.
2. To empty Kibana - import the file without related objects and make sure import works fine.
3. Load esarchive with one index pattern - import a file with just one saved object and ensure Kibana lets us associate the saved object with the index pattern which we loaded and verify its accuracy.
4. Export a dashboard with related objects - change the id of a saved object inside the dashboard - import it back -ensure Kibana behaves accurately

Technical challenges to work through:

• Can import beats dashboards without enabling migration: true in beats.xml
• Need to figure out a place to store saved objects json file
• understand related objects

[bhavyarm]

CC @LeeDr @dmlemeshko

[bhavyarm]

I worked on this and the PR has been merged for a while now - #100828