feat(rum-oversight): improve reduce in skyline

[karlpauls]

In the skyline chart, the aggregates result gets mapped several times.

Description

This patch proposes to only loop one time using a reduce.

Motivation and Context

Speed up the rendering in skyline chart.

How Has This Been Tested?

Looking at the ui rendering speed in the console at

https://skylinereduce--helix-website--karlpauls.hlx.page/tools/oversight/explorer.html?domain=aem.live&domainkey=

[aem-code-sync[bot]]

	Page	Scores	Audits	Google
M	/tools/oversight/explorer.html?domain=aem.live&domainkey=
D	/tools/oversight/explorer.html?domain=aem.live&domainkey=