[8.15] Updates link text on Metrics configuration page (backport #2785)

[mergify]

Overview

Related to https://github.com/elastic/search-docs-team/issues/174
The Metrics app has been renamed to Infrastructure app. This PR updates the link text on the Metrics OOTB jobs page pointing to the Infrastructure app's docs to represent this change. It does not change the metrics job terminology as it remained unchanged. The Infrastructure documentation on the O11y side uses it, too.

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This is an automatic backport of pull request #2785 done by Mergify.

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