feat: Add Google Drive storage backend with custom endpoint support (#613)

* feat: Add Google Drive storage backend with custom endpoint support

- Implement Google Drive storage backend using service account authentication
- Add support for custom Google Drive API endpoints for testing
- Include comprehensive test setup with mock services
- Add configuration options for Google Drive credentials and folder ID
- Update documentation with Google Drive configuration examples

* remove debug messages

* Improve tests

* Add mounting tip on documentation

* Replace deprecated lib usage

* Fix identation

* Fix googledrive tests

* Fix googledrive support for _FILE credentials

* Remove googledrive test unecessary echos

test/googledrive/run.sh

@@ -0,0 +1,59 @@
+#!/bin/sh
+
+set -e
+
+cd "$(dirname "$0")"
+. ../util.sh
+current_test=$(basename $(pwd))
+
+export SPEC_FILE=$(mktemp -d)/googledrive_v3.yaml
+cp googledrive_v3.yaml $SPEC_FILE
+sed -i 's/CREATED_TIME_1/'"$(date "+%Y-%m-%dT%H:%M:%SZ")/g" $SPEC_FILE
+sed -i 's/CREATED_TIME_2/'"$(date "+%Y-%m-%dT%H:%M:%SZ" -d "14 days ago")/g" $SPEC_FILE
+
+docker compose up -d --quiet-pull
+sleep 5
+
+logs=$(docker compose exec backup backup | tee /dev/stderr)
+
+sleep 5
+
+expect_running_containers "4"
+
+if echo "$logs" | grep -q "ERROR"; then
+  fail "Backup failed, check logs for error"
+else
+  pass "Backup succeeded, no errors reported."
+fi
+
+# The second part of this test checks if backups get deleted when the retention
+# is set to 0 days (which it should not as it would mean all backups get deleted)
+BACKUP_RETENTION_DAYS="0" docker compose up -d
+sleep 5
+
+logs=$(docker compose exec -T backup backup | tee /dev/stderr)
+
+if echo "$logs" | grep -q "Refusing to do so, please check your configuration"; then
+  pass "Remote backups have not been deleted."
+else
+  fail "Remote backups would have been deleted: $logs"
+fi
+
+# The third part of this test checks if old backups get deleted when the retention
+# is set to 7 days (which it should)
+BACKUP_RETENTION_DAYS="7" docker compose up -d
+sleep 5
+
+info "Create second backup and prune"
+
+logs=$(docker compose exec -T backup backup | tee /dev/stderr)
+
+if echo "$logs" | grep -q "Pruned 1 out of 2 backups as they were older"; then
+  pass "Old remote backup has been pruned, new one is still present."
+elif echo "$logs" | grep -q "ERROR"; then
+  fail "Pruning failed, errors reported: $logs"
+elif echo "$logs" | grep -q "None of 1 existing backups were pruned"; then
+  fail "Pruning failed, old backup has not been pruned: $logs"
+else
+  fail "Pruning failed, unknown result: $logs"
+fi