create minio bucket automatically on startup (minio-initialize.sh)

Replace the one-shot minio-createbuckets service (which required a
manual 'abra app restart minio-createbuckets' that appeared to hang)
with a minio-initialize.sh config, ported from lasuite-docs. The minio
service entrypoint runs it in the background before starting minio; it
waits for minio to be ready and idempotently creates the
drive-media-storage bucket with versioning. Manual trigger:
'abra app cmd minio minio_initialize'.

abra.sh

@@ -5,6 +5,7 @@ export NGINX_CONF_VERSION=v6
 export ONLYOFFICE_CONF_VERSION=v2
 export PG_BACKUP_VERSION=v4
 export MIGRATE_VERSION=v1
+export MINIO_INITIALIZE_VERSION=v1
 
 environment() {
   # this exports all the secrets as environment variables
@@ -15,6 +16,10 @@ migrate() {
   /migrate.sh
 }
 
+minio_initialize() {
+  /minio-initialize.sh
+}
+
 trigger_wopi() {
   environment
   python manage.py trigger_wopi_configuration