Create docs page on how to install Keptn without a custom metrics exporter

[mowies]

Goal

As a users who already has the prometheus custom metrics exporter on my cluster, I want to still be able to install Keptn and use its full feature set.

Details

Create a docs page that explains how to replace the prometheus custom metrics exporter with the Keptn one and not have any reduction in functionality.

DoD

• page created under the installation/configuration folder in docs-new
• steps reproduced and verified to be working

[mowies]

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