charts/gateway replace find command

[emilytzhang]

Description of the change

Replace find command with du and grep command

Benefits

Works with both centos7 and ubi9-minimal OS

Drawbacks

Applicable issues

• fixes #

Additional information

Checklist

• [x] Chart version bumped in Chart.yaml according to semver.
• [x] Variables are documented in the README.md
• [x] Title of the PR starts with chart name (e.g. [charts/gateway])
• [x] If the chart contains a values-production.yaml apart from values.yaml, ensure that you implement the changes in both files