Rework Tools documentation: find and list all performance-related docs in a single place
To rework our documentation, we have to know what documentation we currently have.
We have many places which are related to performance improvements, best practices, and tools for solving performance-related issues across the whole app.
@rzwambag listed them here: #349958 (comment 843282700)
To make the navigation efficient, we need to index all performance pages across all our docs in a single place, at https://docs.gitlab.com/ee/development/performance.html, which will serve as an entry point.
Note: an issue for creating a guide on "solving a performance issue" was extracted into #356438
Edited by Aleksei Lipniagov