chore(gatsby): Give option to ignore output from workers and silence validate-engines

[imjoshin]

Description

Duplicate/unnecessary output was being seen from the validate-engines worker. This PR gives each worker the ability to ignore output using forks silent option.

Example from validate-engines:

const worker = new WorkerPool<typeof import("./child")>(
  require.resolve(`./child`),
  {
    numWorkers: 1,
    env: {
      // Do not "inherit" this env var for validation,
      // as otherwise validation will fail on any imports
      // that OpenTracing config might make
      GATSBY_OPEN_TRACING_CONFIG_FILE: ``,
    },
    silent: true,
  }
)

Documentation

Documented within the gatsby-worker's README.md.

[sc-39755]

[pieh]

That's great! I really appreciate updating README / docs even tho I didn't mention this part :)