Support custom domain

[kiootic]

For single-site mode, custom domain is supported by usage of PAGESHIP_HOST_PATTERN config.

For unmanaged-sites mode, custom domain is specified in sites.toml. It should be validated to ensure no duplicated custom domain association is present.

For managed-sites mode, custom domain is specified in app section of pageship.toml.

• We use a cooperative model for management of custom domain - we don't perform domain ownership verification.
• Each app can configure multiple custom domains, each custom domain should correspond to exactly one site.
• When configuration is updated and custom domain is changed, an internal domain associaion table is updated.
  • If the domain is already associated with an app, the domain association is not updated automatically. A warning would be shown, and manual activation is needed.
  • Releasing a domain association would not restore it for existing app, existing app need activate manually.
  • Pattern for site matching is not planned for now.
• API & command is available to check the status of the custom domain association at the moment.
  • active/inactive/claimed by another app (with app ID)
• API & command is available to re-activate the custom domain association.

Example flow:

1. App A updates config with custom domain X
2. Custom domain X is associated with app A.
3. App B updates config with custom domain X.
4. A warning is shown due to existing association.
5. Custom domain X is still associated with app A.
6. App B activates the custom domain association.
7. Custom domain X is associated with app B.
8. App A activates the custom domain association.
9. Custom domain X is associated with app A.
10. App A updates config with no custom domain.
11. Custom domain X is inactive.
12. App B activates the custom domain association.
13. Custom domain X is associated with app B.