[#823]: feat(pipes,sockets): allow running scripts in the server's command

## Description of Changes

- ✏️ Remove requirement to share the same PID for the worker and root process. 
According to the fork (and to be precise, `fork-exec` in go) man pages documentation, 

```text
The child inherits copies of the parent's set of open file descriptors.  
Each file descriptor in the child refers to the same open file description (see open(2)) as the corresponding file descriptor in the parent. 
This means that the two file descriptors share open file status flags, file offset, and signal-driven I/O attributes (see the description of F_SETOWN and F_SETSIG in fcntl(2)).
```

- ✏️ Server plugin can accept scripts (sh, bash, etc) in it's `command` configuration key:
```yaml
server:
    command: "./script.sh OR sh script.sh" <--- UPDATED
    relay: "pipes"
    relay_timeout: "20s"
```
The script should start a worker as the last command. For the `pipes`, scripts should not contain programs, which can close `stdin`, `stdout` or `stderr`.

1 files changed, 2 insertions, 0 deletions

diff --git a/tests/socket_test_script.sh b/tests/socket_test_script.sh
new file mode 100755
index 00000000..3948c4fb
--- /dev/null
+++ b/tests/socket_test_script.sh
@@ -0,0 +1,2 @@
+#!/usr/bin/env bash
+php ../../tests/client.php echo tcp