[Dashboard] Replace labs:dashboard:deferBelowFold advanced setting with dashboard option

[nreese]

Blocked by #148933

labs:dashboard:deferBelowFold was added by #99880 in May 2021. This is a great feature that is hidden behind a labs flag and lightly used.

We discussed the following options for promoting the setting out of labs:

• Remove lab setting and load all dashboards with defer below the fold.
  • rejected because some users may load dashboard, get coffee and return to computer and expect the entire dashboard to have loaded
• Promote labs:dashboard:deferBelowFold out of labs and keep as advanced setting dashboard:deferBelowFold
  • rejected because feature would remain hidden/seldom used
• Remove feature entirely
  • rejected because feature has value on limiting workload of elasticsearch cluster and allowing visible part of screen to load faster

labs:dashboard:deferBelowFold flag should be removed and replaced with a dashboard option so that loading can be configured per dashboard by the dashboard author.

[teresaalvarezsoler]

@nreese Thanks for the thorough thinking and the transparency on the decisions made.

In order for the visualizations "below fold" to load, do we need to make all the queries again to Elasticsearch (i.e., users will have to wait the entire time to connect to the cluster, etc.) or do we already have the data and it is just a matter of rendering the visualizations, applying formulas, etc.?

[nreese]

In order for the visualizations "below fold" to load, do we need to make all the queries again to Elasticsearch (i.e., users will have to wait the entire time to connect to the cluster, etc.) or do we already have the data and it is just a matter of rendering the visualizations, applying formulas, etc.?

Any panel below the page edge is not loaded until users scroll down and the panel is in the visible portion of the page. This means that data is not fetched until the panel is in view. This has the benefit of speeding up loading of visible panels since there are fewer requests sent to elasticsearch.

[teresaalvarezsoler]

Remove lab setting and load all dashboards with defer below the fold.
rejected because some users may load dashboard, get coffee and return to computer and expect the entire dashboard to have loaded

Can we first load the visible panels and the non-visible ones afterwards (without requiring the user to scroll)? That way all the panels will load even if the user is not making "focus" on them.

[nreese]

Can we first load the visible panels and the non-visible ones afterwards (without requiring the user to scroll)? That way all the panels will load even if the user is not making "focus" on them.

I am sure that could be accomplished, but that is not how the feature works today.

[andremacola]

Related to #176535