Add FabricBot config

[davidbritch]

This FabricBot configuration uses three tasks to auto-merge main to live, when there's a difference between the two branches. It:

1. Creates a PR, every three hours, if there's a difference between main and live. I was going to set this to every 12 hours, or once a day, but me editing the config results in it using the GMT timezone. I figure you'll want to use PST/EST or similar.
2. Adds the auto-merge label to any PRs going into live. The consequence is that we shouldn't ever manually create PRs that target live.
3. Auto-merges any PRs to live that have the auto-merge label. The repo is setup so that the only people who can merge to live are admins and FabricBot. Note, this uses a merge rather than a squash merge. The approach for docs repos is to squash merge into main, and merge into live.

This is currently identical to the config for dotnet-maui-api-docs.

The config can be changed by importing fabricbot.json into https://aka.ms/fabricbotconfig

[opbld31]

Learn Build status updates of commit 43f0918:

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.github/fabricbot.json	✅Succeeded

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