Schema Validations: Identify tables that do not match schema

What does this MR do and why?

I'm splitting MR !115066 (closed).

Adds table support to Gitlab::Database::SchemaValidation framework

It adds the two new validators:

• ExtraTables: Check if tables are present in the db, but not in the structure.sql file;
• MissingTables: Check if tables are present in the structure.sql file, but not in the db;

Code is not DRY. We're still validating the framework. We're planing a refactoring soon as we validate the idea.

See: !113317 (comment 1304807919)

How to set up and validate locally

Testing ExtraTables (tables that are present in the Database and not in the structure.sql)

1. Remove a table definition from structure.sql, like CREATE TABLE lfs_objects (id integer NOT NULL, ...)
2. Check if the lfs_objects table is present in ExtraTables output:

structure_sql = Gitlab::Database::SchemaValidation::StructureSql.new(Rails.root.join('db/structure.sql'), 'public')
database = Gitlab::Database::SchemaValidation::Database.new(ActiveRecord::Base.connection)
Gitlab::Database::SchemaValidation::Validators::ExtraTables.new(structure_sql, database).execute

Check the output

The table lfs_objects is present in the database, but not in the structure.sql file
Diff:
+id integer NOT NULL, oid character varying NOT NULL, size bigint NOT NULL, new_updated_at timestamp without time zone, file character varying, file_store integer DEFAULT 1

Testing MissingTables (that are present in the structure.sql and not in the Database)

1. Drop a table from database, like DROP TABLE lfs_objects CASCADE;
2. Check if the lfs_objects table is present in MissingTables output:

structure_sql = Gitlab::Database::SchemaValidation::StructureSql.new(Rails.root.join('db/structure.sql'), 'public')
database = Gitlab::Database::SchemaValidation::Database.new(ActiveRecord::Base.connection)
Gitlab::Database::SchemaValidation::Validators::MissingTables.new(structure_sql, database).execute

Check the output

The table lfs_objects is missing from the database
Diff:
-id integer NOT NULL, oid character varying NOT NULL, size bigint NOT NULL, created_at timestamp without time zone, updated_at timestamp without time zone, file character varying, file_store integer DEFAULT 1

MR acceptance checklist

This checklist encourages us to confirm any changes have been analyzed to reduce risks in quality, performance, reliability, security, and maintainability.

• I have evaluated the MR acceptance checklist for this MR.

Related to #388013 (closed)