[bitnami/external-dns] feat: add support to namespaceOverride and simplify name helpers

[juan131]

Description of the change

This PR adds support for using the namespaceOverride parameter (common in the catalog) to override the target namespace where to install the chart.

It also incorporates the usage of some helpers from "common" chart so custom ones are no longer necessary such as common.names.name or common.names.fullname.

Benefits

Standardization

Possible drawbacks

None

Applicable issues

• fixes https://github.com/bitnami/charts/issues/30497

Additional information

N/A

Checklist

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