Add getter and setter for connection in the DatabaseBatchRepository class

[abrardev99]

This simple PR adds setConnection and getConnection methods in the DatabaseBatchRepository class.

Why

In the tenancy package, We are adding support for Laravel job batches which required temporarily replacing the BatchRepository connection with the correct tenant connection and then reverting it back when exiting the tenant context.

The current implementation uses the PHP Reflection class. It would be nice to have these methods in the framework to get rid of the Reflection boilerplate and modify the connection easily.

Wondering how our code would look:

Before

$batchRepositoryReflection = new ReflectionClass($batchRepository);
$connectionProperty        = $batchRepositoryReflection->getProperty('connection');
$connectionProperty->setAccessible(true);
$connection = $connectionProperty->getValue($batchRepository);

$this->previousConnection = $connection;

$connectionProperty->setValue($batchRepository, DB::connection('tenant'));

After

$this->previousConnection = $batchRepository->getConnection();
$batchRepository->setConnection(DB::connection('tenant'));

Tests

I haven't added tests because, as I said, these are simple changes, not a feature. I'm not sure if we need tests for getters and setters. If still wants me to add tests, please comment, and I'll add them.