store custom app certificates in subdomains table

the REST route and model code is still ununsed as before since there
is no way to set the certs from the UI.

migrations/schema.sql

@@ -157,7 +157,7 @@ CREATE TABLE IF NOT EXISTS domains(
     tlsConfigJson TEXT, /* JSON containing the tls provider config */
     wellKnownJson TEXT, /* JSON containing well known docs for this domain */
 
-    fallbackCertificateJson TEXT,
+    fallbackCertificateJson MEDIUMTEXT,
 
     PRIMARY KEY (domain))
 
@@ -210,6 +210,8 @@ CREATE TABLE IF NOT EXISTS subdomains(
     subdomain VARCHAR(128) NOT NULL,
     type VARCHAR(128) NOT NULL, /* primary or redirect */
 
+    certificateJson MEDIUMTEXT,
+
     FOREIGN KEY(domain) REFERENCES domains(domain),
     FOREIGN KEY(appId) REFERENCES apps(id),
     UNIQUE (subdomain, domain));