[Reporting/Dashboard] Newly loaded Sample Data dashboard must be explicitly saved before user can copy POST URL

[tsullivan]

Kibana version: 7.16.0-SNAPSHOT

Describe the bug:
User incorrectly sees a message that the POST URL is too long and is unable to be copied.

Steps to reproduce:

1. Install the flights dataset of sample data
2. Once install is complete, click "Dashboard": https://user-images.githubusercontent.com/908371/140835590-dc393936-79ce-49a8-99cd-c6cccabeef11.png
3. Click "Share" > "PDF Reports" > "Advanced options"

Expected behavior:
User should see a blue "Copy POST URL" button

There seems to be a workaround: after clicking Edit > Save, the correct behavior takes over and the user can click the "Copy POST URL" button.

Notes
As of this PR: #114331 the URL of a "saved" dashboard should never be too long to copy. Perhaps something about the way the dashboard is loaded makes the workaround needed.

[elasticmachine]

Pinging @elastic/kibana-presentation (Team:Presentation)

[tsullivan]

@jloleysens and I chatted with @ThomThomson and we now understand the impact of this bug. It is very low impact, as it only affects the sample data dashboards.

It shouldn’t be possible for this to show up in a user’s dashboard. The reason the demo data is like this is because the map was saved into the dashboard without a mapBuffer which is because the saved object was manually written a while ago and hasn’t been subjected to migrations. That means that the entire panels part of the dashboard state is getting into the URL, which could definitely make it bigger than 25k characters.