Convert unique keys in 3 tables to primary keys (#115421)

* Added method for adding migrations for convering unique to primary key.

Based on existing migration for `file` table (in `db_file_storage.go`) migrations.

* Added better default migration names. Added ability to override migration name.

* Use ConvertUniqueKeyToPrimaryKey for cloud_migration_snapshot_partition table.

* Convert resource_version UQE to PK.

* Convert secret_encrypted_value UQE to PK.

* Removed extra test.

* Removed testdata.

* Remove support for renaming migrations for now. We can bring it in later, when we want to convert existing migrations for file, file_meta and setting tables.

* Revert removal of ColumnName to ease backporting, since this field is referenced from enterprise code.

* Use quoted identifiers in Postgres statement.

pkg/services/sqlstore/migrator/testdata/sqlite_file_migration_statement.sql

@@ -0,0 +1,23 @@
+CREATE TABLE IF NOT EXISTS `file_new` (
+    `path` TEXT NOT NULL
+    , `path_hash` TEXT NOT NULL
+    , `parent_folder_path_hash` TEXT NOT NULL
+    , `contents` BLOB NOT NULL
+    , `etag` TEXT NOT NULL
+    , PRIMARY KEY ( `path_hash`,`etag` ));
+
+INSERT INTO `file_new` (`path`
+  , `path_hash`
+  , `parent_folder_path_hash`
+  , `contents`
+  , `etag`)
+SELECT `path`
+  , `path_hash`
+  , `parent_folder_path_hash`
+  , `contents`
+  , `etag`
+FROM `file`;
+
+DROP TABLE IF EXISTS `file`;
+ALTER TABLE `file_new` RENAME TO `file`;
+CREATE INDEX `IDX_file_parent_folder_path_hash` ON `file` (`parent_folder_path_hash`);