feature: allow specifying raw command

[rustatian]

Reason for This PR

closes: roadrunner-server/roadrunner#1667

Description of Changes

• Allow raw command with []string of command parts. There are no breaking changes for config or RR. Command (for server.command, server.on_init, server.after_init, pool.command, pool.after_init) can be specified as string or array where the 0-th element of the array is executable and all other arguments are passed to the executable (binary).

Configuration sample:

server:
  command: ["/Application Support/php", "../rr-e2e-tests/php_test_files/php-test.php"]
  relay: pipes

License Acceptance

By submitting this pull request, I confirm that my contribution is made under
the terms of the MIT license.

PR Checklist

[Author TODO: Meet these criteria.]
[Reviewer TODO: Verify that these criteria are met. Request changes if not]

• All commits in this PR are signed (git commit -s).
• The reason for this PR is clearly provided (issue no. or explanation).
• The description of changes is clear and encompassing.
• Any required documentation changes (code and docs) are included in this PR.
• Any user-facing changes are mentioned in CHANGELOG.md.
• All added/changed functionality is tested.