Added $opts array for customize gRPC client options

[aneterial]

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Pull request type

Please check the type of change your PR introduces:

• Feature

What is the current behavior?

Issue Number: #136

What is the new behavior?

You can customize the gRPC client's behavior by setting options in config array

Example of using:

$config = [
    // ...
    'opts' => [
        'grpc.max_receive_message_length' => 8*1024*1024,
        'grpc.default_compression_algorithm' => 2,
        'grpc.default_compression_level' => 2,
    ],
]
$ydb = new \YdbPlatform\Ydb\Ydb($config);

[rekby]

Hello @aneterial.

Thanks for the PR.
Great job!

I have few small comments for it.

[rekby]

@aneterial thanks for the PR :)