Expose coverage/exec_sec for libfuzzer targets via CLI

[bmc-msft]

Adds debug subcommands to the SDK/CLI that simplify querying Application Insights for libfuzzer telemetry.

Querying for the latest execs_sec for a job, by job_id fragment.

$ onefuzz debug job libfuzzer_execs_sec 88 --limit 1
[
    {
        "execs_sec": "191035",
        "machine_id": "b2dbe720-4fd8-4342-957a-6cb0979d2187",
        "timestamp": "2020-11-18T00:08:53.98Z",
        "worker_id": "0"
    }
]

Querying for the latest coverage for a job, by job_id fragment.

$ onefuzz debug job libfuzzer_coverage 88 --limit 1
[
    {
        "covered": "10",
        "features": "21",
        "rate": "0.47619047619047616",
        "timestamp": "2020-11-18T00:09:40.793Z"
    }
]

[ghost]

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