Persist two singleton entities in SQL tables (#860)

* Persist two singleton entities in SQL tables

A table might not be the best place to store singleton entities, but by
doing this we ensure we can easily inspect them later and use the same
sort of persistence logic for these that we do elsewhere.

ServerSecret is stored upon retrieval so that we make sure that the same
secret is used in both Datastore and SQL (we wouldn't want to change
it).

* Responses to CR

* Don't have a separate ID for the singleton entities

* Rename secret UUID

* Rename and regenerate

db/src/main/resources/sql/schema/db-schema.sql.generated

@@ -626,6 +626,11 @@
         primary key (revision_id)
     );
 
+    create table "ServerSecret" (
+       secret uuid not null,
+        primary key (secret)
+    );
+
     create table "SignedMarkRevocationEntry" (
        revision_id int8 not null,
         revocation_time timestamptz not null,
@@ -692,6 +697,13 @@
         primary key (tld_name)
     );
 
+    create table "TmchCrl" (
+       certificate_revocations text not null,
+        update_timestamp timestamptz not null,
+        url text not null,
+        primary key (certificate_revocations, update_timestamp, url)
+    );
+
     create table "Transaction" (
        id  bigserial not null,
         contents bytea,