[FR] Update ActionCodeSettings to support link_domain

[huwmartin]

Is your feature request related to a problem? Please describe.

Firebase Dynamic Links will stop working August 25th 2025.

Migration instructions indicate that to use a custom domain one should update usage of ActionCodeSettings to use linkDomain, see also in the Firebase Admin docs.

We currently depend upon firebase-admin-python generate_sign_in_with_email_link to generate email links, firebase-admin-python hasn't been updated with link_domain and currently only supports dynamic_link_domain, firebase-admin-node has been updated with support for linkDomain so I assume this should be officially supported, please let me know if this is not the case.

Describe the solution you'd like

ActionCodeSettings should be updated to accept link_domain and encode_action_code_settings should be updated to handle link_domain.

[google-oss-bot]

I couldn't figure out how to label this issue, so I've labeled it for a human to triage. Hang tight.

[huwmartin]

Opened a PR for this here #884