[charts/portal] Custom domain and vanityURL

[cuisimon]

Add support for custom domain certificates in the Dispatcher component by introducing:

• Accepts certificate and key files via Helm command line using --set-file
• Creates a Kubernetes Secret to store all custom domain certificates and keys
• Updates the dispatcher template to read certificates and keys from the secret
• Maintains the same environment variable naming pattern (CD_{TENANT}_ZZ_{DOMAIN}_CERT and CD_{TENANT}_ZZ_{DOMAIN}_KEY)
• CUSTOM_URLS_ENABLED - Boolean flag to enable/disable custom URLs feature
• CD_{TENANT}_ZZ_{DOMAIN}_CERT - Base64-encoded certificate for each tenant/domain combination
• CD_{TENANT}_ZZ_{DOMAIN}_KEY - Base64-encoded key for each tenant/domain combination
• The CD_* variables are only set when CUSTOM_URLS_ENABLED is true.

Benefits

Fixe DE641541: Change hostname/domainname of tenant exiting portal tenant

Drawbacks

None.

Applicable issues

• DE641541: Change hostname/domainname of tenant exiting portal tenant

Additional information

Checklist

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