chore: use #!/usr/bin/env bash in all scripts

More portable than #!/bin/bash — resolves bash from PATH,
which handles installations outside /bin (e.g. Homebrew on macOS).

dbdump_mongo/db-dump.sh

@@ -1,4 +1,4 @@
-#!/bin/bash
+#!/usr/bin/env bash
 
 # Author: Julien Gautier <jgautier.webdev@gmail.com>
 # Organization: AdAstra

dbrestore_mongo/db-restore.sh

@@ -1,4 +1,4 @@
-#!/bin/bash
+#!/usr/bin/env bash
 
 # Author: Julien Gautier <jgautier.webdev@gmail.com>
 # Organization: AdAstra

dbutils_mongo/db-start.sh

@@ -1,4 +1,4 @@
-#!/bin/bash
+#!/usr/bin/env bash
 
 # Author: Julien Gautier <jgautier.webdev@gmail.com>
 # Organization: AdAstra