fix(lagoon): keep Status plugin-only; migrate:status adds the framework sets itself (WR-12)

57a849d made lagoon.Status read migrationSets, which changed its result
for consumers: the framework sets came first and a plugin with no
migrations lost its row. Status is back to its pre-57a849d behaviour.
migrate:status (table and --json) now reads the unexported setStatus,
which lists the framework sets and the plugins from migrationSets, so it
still agrees with migrate --pretend. Both share historyRows.

- TestStatusPluginRows pins Status: plugin rows only, an empty row for a
  plugin with no migrations or no history table, none without HasMigrations
- TestMigrateStatusJSON also checks the table lists the framework sets
- TestTwoPluginMigrationSetsIsolated and TestDocsMigrate are back to the
  plugin-only rows

docs/database/migrations.md

@@ -104,6 +104,8 @@ if err := lagoon.RollbackLast(db, plugins, "acme.blog"); err != nil {
 
 `lagoon.Migrate`, `lagoon.Status` and `lagoon.RollbackLast` take the activated plugins; a plugin that does not implement `pact.HasMigrations` is skipped.
 
+`lagoon.Status` returns one row per plugin, a plugin with no migrations included, and leaves out the framework's own sets that `migrate:status` prints.
+
 ## Porting version.yaml
 
 WinterCMS runs a plugin's update scripts by version number and seeds data from the same files. When you port a plugin: