feat(config): Add an option to prevent interpolation of env vars within config loading process

[graphcareful]

Summary

Add an option to prevent interpolation of env vars within config loading process. Useful for when the config value may contain reserved symbols such as "$" which would make Vector go and replace those values with values from the global environment. Behavior is to default to "on" which would not be a breaking change for existing users.

How did you test this PR?

Use this option

--disable-env-var-interpolation
  Disable interpolation of environment variables in configuration files

  [env: VECTOR_DISABLE_ENV_VAR_INTERPOLATION=]

Config:

sources:
  in:
    type: demo_logs
    format: json
transforms:
  tr:
    type: sample
    inputs:
      - in
    rate: "$RATE"
sinks:
  out:
    type: blackhole
    inputs:
      - tr

And in global environment, set RATE=12

Change Type

• Bug fix
• New feature
• Non-functional (chore, refactoring, docs)
• Performance

Is this a breaking change?

• Yes
• No

Does this PR include user facing changes?

• Yes. Please add a changelog fragment based on our guidelines.
• No. A maintainer will apply the no-changelog label to this PR.

References

Notes

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[pront]

I wonder if we want to do this check inside prepare_input which is implemented in src/config/loading/mod.rs. IIRC all prepare implementations delegate to that.

[graphcareful]

I'll take a look at that