Added support for custom hosts/domains for auto devops

What does this MR do?

This MR adds the variable ADDITIONAL_HOSTS to the Auto DevOps template which sets the Helm chart variable service.additionalHosts created by charts/auto-deploy-app!20 (merged). The variable <ENVIRONMENT>_ADDITIONAL_HOSTS can also be specified and takes precedence. It allows specification of additional hosts via a comma-separated list such as domain.com, www.domain.com.

What are the relevant issue numbers?

Closes #46954 (closed)

Does this MR meet the acceptance criteria?

• Changelog entry added, if necessary
• Documentation created/updated
• Tests added for this feature/bug
• Tested in all supported browsers
• Conforms to the code review guidelines
• Conforms to the merge request performance guidelines
• Conforms to the style guides
• Conforms to the database guides
• Link to e2e tests MR added if this MR has Requires e2e tests label. See the Test Planning Process.
• Security reports checked/validated by reviewer