[6.x] Fix Cache store with a name other than 'dynamodb'

[deleugpn]

This pull request partially reverts changes introduced in #36749 (ping @driesvints).

The problem particularly is located here: a20c9e5#diff-5c56e532b7bf21453188f98f7999ed558eff31a6374ebd83c9f811961fde02b1R37

It is forcing applications to reserve the cache.stores.dynamodb as the only way to configure an AWS DynamoDb Client instance. If, for instance, we rename dynamodb in our application to anything else, then the region, key and secret won't take effect because it will rely on the DynamoDb Client bound by cache.stores.dynamodb. The consequences of relying on this binding are:

• Applications cannot rename dynamodb on the cache configuration.
• Applications cannot have 2 or more dynamodb cache configurations which are not in the same region / access key / secret key.
• A secondary cache not called dynamodb will still use the region and access configured for the dynamodb key.

By reverting that, we bring control back to users so that they're free to change the skeleton configuration without invisible side effects.

For my particular use-case, I created a Cache Store configuration called session and then configured it as follows:

        'session' => [
            'driver' => 'dynamodb',
            'region' => env('AWS_REGION'),
            'table' => env('DYNAMODB_SESSION_TABLE'),
        ],

This means that access is determined by IAM Role (assume role) instead of key and secret. I also configured session.store as session so that Laravel's Session is managed by the Cache Store called session. This is how I detected the problem.

[driesvints]

@deleugpn Thanks for fixing this!

[deleugpn]

My pleasure!