How do I include a custom module translation? I have a Drupal 8 custom module (custom_module) and a custom_module-8.x-1.0.da.po file I added to sites/default/files/translations, but my translations are not getting Imported during the module installation, even though translations are available for import in admin/reports/translations. Am I missing any step?

I don't want to put my custom_module-8.x-1.0.da.po file in sites/default/files/translations; I prefer it to be inside the module directory, if possible.
Add interface translation project and interface translation server pattern definitions to custom_module.info.yml.
You can use a custom path for your translation po file by setting the interface translation server pattern to whatever you want.