Config format V2

[brendan-kellam]

This PR introduces a new configuration schema that is more expressive.

Example config:

{
    "repos": [
        {
            "type": "github",
            "token": "secret-token",
            "orgs": [
                "sourcebot-dev",
                "commaai"
            ],
            "users": [
                "DHH"
            ],
            "repos": [
                "torvalds/linux",
                "my-org/my-repo"
            ],
            "exclude": {
                "repos": [
                    "sourcebot-dev/sourcebot"
                ],
                "archived": true,
                "forks": true
            }
        },
        {
            "type": "gitlab",
            "token": "secret-token",
            "groups": [
                "my-group"
            ],
            "users": [
                "user1",
                "user2"
            ],
            "projects": [
                "my-group/project1",
                "my-group/my-sub-group/project2"
            ],
            "exclude": {
                "projects": [
                    "my-group/my-project3"
                ],
                "archived": true,
                "forks": true
            }
        }
    ]
}

With the new configuration schema comes a new index server, located in packages/backend. This has the same functionality as zoekt-indexserver (it will clone repos and periodically re-index them), but with improved logging s.t., it's now easier to determine what the index server is doing.

Fixes #35
Fixes #27

[msukkari]

🔥🔥🔥 tested working on my side (public/private github and gitlab, as well as self-hosted gitlab)