WIP web: Combine repository setting pages

Created by: keegancsmith

As part of removing enabled/disabled state the landing page for repository settings has much less information to show. So the decision was made to combine all the pages into one. This commit naively combines all the current pages without doing any adjustments as mentioned in the design.

Part of #2025 (closed)

Test plan: Visit the settings page in development mode. Will also visit page with indexing disabled.

Design

This is a WIP, so we are still far off from the design. Additionally this PR will not implement the external service cards. That will be another PR. See comments images of current state.

Sourcegraph Engineer / Design Spec Link: https://zpl.io/anpXvGr Public / Non-Engineer Design Link: https://sketch.cloud/s/wwoGV/Axae1bR/play