fix: read config process output before waiting exit code #2528

[ivanzamanov]

Summary:

Fixes #2528

Read config process output before awaiting exit code, thus allowing output larger than the OS pipe buffer to be output.

Test Plan:

Simply make sure output from the config process is read correctly even if output exceeds the buffer size.

Checklist

• [x] Documentation is up to date to reflect these changes.
• [x] Follows commit message convention described in CONTRIBUTING.md

[cortinico]

The logic in this file is not used anymore in 0.75/0.76 and is kept only for compatibility. We should probably remove it from this repo.