[Reporting] Provide a way to customize height for the reporting

[dej611]

Describe the feature:

As identified by the investigation in #154894 (comment) reporting is ignoring any passed height size and use a 1200px which becomes an effective ~1086px min height on the final report.
Dashboard is less affected by this problem as usually there are few panels in it, but for some single visualization within the Lens editor (say a Metric or a Gauge) a smaller height can be useful.

Describe a specific use case for the feature:

[elasticmachine]

Pinging @elastic/appex-sharedux (Team:SharedUX)

[tsullivan]

I'm not sure there is a way to solve this without fundamentally changing how screenshotting works.

Currently we only use the width parameter to set the width of the headless browser window when the report executes. But, we capture everything in the visualization's DOM element, even pixels that are "below the fold." Therefore the height field from the report job's layout parameters ends up not being used.

Basically, if a smaller height is needed, then the application would need to render the visualization using a smaller height somehow.