Introduce Lighthouse Backend with Scheduling of Audits

Signed-off-by: Dominik Pfaffenbauer <dominik@pfaffenbauer.at>

.changeset/cool-spoons-bathe.md

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+---
+'@backstage/plugin-lighthouse-backend': minor
+---
+
+Introduce Lighthouse Backend Plugin to run scheduled Lighthouse Audits

.changeset/eight-vans-drum.md

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+---
+'@backstage/plugin-lighthouse-common': minor
+---
+
+Introduce @backstage/plugin-lighthouse-common with the API implementation

.changeset/fluffy-books-tickle.md

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+---
+'example-backend': minor
+---
+
+Add Lighthouse Backend to Example Backend

.changeset/young-beans-float.md

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+---
+'@backstage/plugin-lighthouse': minor
+---
+
+Require @backstage/plugin-lighthouse-common package where API implementation moved to