feat: use shfmt to find shellscripts

mentioned in commit 4b6f0370

mentioned in merge request gitlab-com/runbooks!5330 (merged)

mentioned in merge request gitlab-org/release-tools!2136 (merged)

mentioned in merge request cmbr!145 (merged)

mentioned in merge request pmv!212 (merged)

mentioned in merge request third-party-container-images!28 (merged)

mentioned in merge request bigquery-loader!62 (merged)

mentioned in merge request terra-transformer!193 (merged)

mentioned in merge request asdf-gl-infra!27 (merged)

mentioned in merge request common-ci-tasks-images!53 (merged)

mentioned in merge request fluentd-docker!36 (merged)

mentioned in merge request es-diagnostics!15

mentioned in merge request gitlab-com/gl-infra/k8s-workloads/common!241 (merged)

mentioned in merge request slackline!136 (merged)

mentioned in merge request gitlab-com/gl-infra/platform/runway/runwayctl!2 (merged)

mentioned in merge request gcp-quota-exporter!2 (merged)

mentioned in merge request es-diagnostics!18 (closed)

mentioned in merge request es-diagnostics!21