Convert script shebangs from "#!/bin/bash" to "#!/usr/bin/env bash"

This is especially important for distributions like NixOS where `/bin/bash` doesn't exist, or for MacOS users who've installed a newer version of Bash than the one that comes with their OS.

Signed-off-by: Andrew "Tianon" Page <admwiggin@gmail.com>
Upstream-commit: e6a4e7507c
Component: cli

components/cli/docs/reference/builder.md

@@ -1029,7 +1029,7 @@ the final executable receives the Unix signals by using `exec` and `gosu`
 commands:
 
 ```bash
-#!/bin/bash
+#!/usr/bin/env bash
 set -e
 
 if [ "$1" = 'postgres' ]; then