Introduce NL_LOG to control logging format

[adam-singer]

Description

NL_LOG envionment variable is used to control the logging format that tracing_subscriber emits out. We currently want to allow for better ingestion of formatted logs in json.

NL_LOG can be configured with pretty, json, or compact. See Format for more detail on console logging format configurations for tracing_subscriber.

Fixes #1153

Type of change

Please delete options that aren't relevant.

• New feature (non-breaking change which adds functionality)

How Has This Been Tested?

Run from console to see the different log formats

Default

$ cargo run --bin nativelink -- nativelink-config/examples/basic_cas.json
     Running `target/debug/nativelink nativelink-config/examples/basic_cas.json`
  2024-07-13T05:38:08.874357Z  WARN nativelink: Ready, listening on 0.0.0.0:50051
    at src/bin/nativelink.rs:677

  2024-07-13T05:38:08.874826Z  WARN nativelink: Ready, listening on 0.0.0.0:50061
    at src/bin/nativelink.rs:677

  2024-07-13T05:38:08.879914Z  WARN nativelink_worker::local_worker: Worker registered with scheduler, worker_id: 8e0703dc-73c3-428f-a3c4-6dbebaafd0f7
    at nativelink-worker/src/local_worker.rs:558
    in nativelink::worker with name: "worker_0"

Json

$ NL_LOG=json cargo run --bin nativelink -- nativelink-config/examples/basic_cas.json
     Running `target/debug/nativelink nativelink-config/examples/basic_cas.json`
{"timestamp":"2024-07-13T05:38:25.159897Z","level":"WARN","fields":{"message":"Ready, listening on 0.0.0.0:50051"},"target":"nativelink"}
{"timestamp":"2024-07-13T05:38:25.160350Z","level":"WARN","fields":{"message":"Ready, listening on 0.0.0.0:50061"},"target":"nativelink"}
{"timestamp":"2024-07-13T05:38:25.164892Z","level":"WARN","fields":{"message":"Worker registered with scheduler","worker_id":"73cf46ea-c58c-480a-bf4f-bd792ced4f1d"},"target":"nativelink_worker::local_worker","span":{"name":"\"worker_0\"","name":"worker"},"spans":[{"name":"\"worker_0\"","name":"worker"}]}

compact

$ NL_LOG=compact cargo run --bin nativelink -- nativelink-config/examples/basic_cas.json
     Running `target/debug/nativelink nativelink-config/examples/basic_cas.json`
2024-07-13T05:38:34.098568Z  WARN nativelink: Ready, listening on 0.0.0.0:50051
2024-07-13T05:38:34.099017Z  WARN nativelink: Ready, listening on 0.0.0.0:50061
2024-07-13T05:38:34.104507Z  WARN worker: nativelink_worker::local_worker: Worker registered with scheduler worker_id=bf440d8a-8dab-4fe1-8683-1e40469b87c2 name="worker_0"

Checklist

• bazel test //... passes locally
• PR is contained in a single commit, using git amend see some docs

---

This change is 

[allada]

Reviewed 2 of 2 files at r1, all commit messages.
Reviewable status: 1 of 1 LGTMs obtained, and pending CI: Analyze (javascript-typescript), Analyze (python), Bazel Dev / ubuntu-22.04, Cargo Dev / macos-13, Cargo Dev / ubuntu-22.04, Installation / macos-13, Installation / macos-14, Installation / ubuntu-22.04, Local / ubuntu-22.04, Publish image, Publish nativelink-worker-init, Publish nativelink-worker-lre-cc, Remote / large-ubuntu-22.04, asan / ubuntu-22.04, docker-compose-compiles-nativelink (20.04), docker-compose-compiles-nativelink (22.04), integration-tests (20.04), integration-tests (22.04), macos-13, pre-commit-checks, ubuntu-20.04 / stable, ubuntu-22.04, ubuntu-22.04 / stable, windows-2022 / stable