[Index] Make sync-chart-cloudflare-index more resilient

[migruiz4]

Description of the change

Improves the 'sync-chart-cloudflare-index.yml' workflow by implementing a retry mechanism and a integrity check.

Benefits

These changes aim to prevent the recent index failures, which we suspect may be related to the upload of the index.yaml

Additional information

Changes implemented:

• Added --fail flag to the curl command.

• Added --max-time 10 to limit the command.

• Retry after 20 seconds, if the curl failed.

• Retry if the integrity check fails. The integrity check compares the local index md5sum to the index available at 'http://charts.bitnami.com/bitnami/index.yaml'. The integrity check waits 20 seconds to ensure synchronization.

• Notify if the max number of retries (3) have been exceeded.

• Fixes Repository invalid? skipping loading invalid entry for chart "airflow" "" from https://charts.bitnami.com/bitnami: validation: chart.metadata.name is require #31350

Checklist

• Chart version bumped in Chart.yaml according to semver. This is not necessary when the changes only affect README.md files.
• Variables are documented in the values.yaml and added to the README.md using readme-generator-for-helm
• Title of the pull request follows this pattern [bitnami/<name_of_the_chart>] Descriptive title
• All commits signed off and in agreement of Developer Certificate of Origin (DCO)