fix(insights): When exporting to PNG respect the show_legend display option

[vdekrijger]

Problem

During my recent clickthrough spree of our application, we noticed that the export > png function does not include the legends (even if they have been enabled through the display option) for insights.

Whilst I was working on the TF export for our hackathon at the offsite, I was going through our exporter logic and discovered the issue with the PNG exports not having the legends set. In order to catch 2 birds with one stone, I figured I would update that as well.

Changes

1. We pass the show legend display option to the backend through the export_context (similar to how we do this for some other models, example for heatmaps).
2. The backend then fetches this field (if present) whilst building the details for the insight exports and passes it on to the export endpoint through a GET parameter.

How did you test this code?

1. Run the Posthog application locally
2. Create an insight (ensuring there is no legend)
3. Run the png export and confirm that there is no legend in the export
4. Adjust the display options, setting the Show Legend to true
5. Run the png export and confirm that this time, there is a legend on the export
6. Also ran an export of the dashboards to confirm it's all okay
7. And finally ran an export of the shared page for an insight with / without the show legend option enabled.

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Without the legend being set

With the legend being set

(this already worked on master, but it's here for completeness sake)

Changelog: (features only) Is this feature complete?

[github-actions]

Size Change: +65 B (0%)

Total Size: 3.43 MB

ℹ️ View Unchanged

Filename	Size	Change
frontend/dist/toolbar.js	3.43 MB	+65 B (0%)

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[vdekrijger]

The legend parameter originated from this commit: 16e62f1#diff-588e33fbae1f1b86bfbd786002306364c5c240840ac3f148e7ed7634c34efbbdR80.

Due to it not having a true / false value and it just being a name, Python will interpret it as a falsy value (in fact, I think most backend languages do this) and therefore the legend won't be shown.

We have another check here:

posthog/frontend/src/exporter/ExportedInsight/ExportedInsight.tsx

Lines 36 to 45 in 5992ae8

	if (
	isInsightVizNode(insight.query) &&
	isTrendsQuery(insight.query.source) &&
	insight.query.source.trendsFilter &&
	insight.query.source.trendsFilter.showLegend == true
	) {
	// legend is always shown so don't show it alongside the insight
	insight.query.source.trendsFilter.showLegend = false
	}

however that check appears to be responsible for whether or not to show the legend on the sidebar, thus having it being disabled there is a good thing to avoid either 2 legends showing up.

[greptile-apps]

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