fix(spanner): Explicit declaration of dependencies for OpenTelemetry traces sample

[nareshz]

This PR includes changes to add all the required dependencies for OpenTelemetry traces sample explicitly.

[Sita04]

@minherz PTAL at these changes.

[nareshz]

@olavloite Can you PTAL at your convenience?

[nareshz]

what is a reason for adding all these dependencies? is it the best practice to be followed?

Yes, right. The reason is mainly to follow good practice of explicitly declaring all the dependencies required.

[minherz]

what is a reason for adding all these dependencies? is it the best practice to be followed?

Yes, right. The reason is mainly to follow good practice of explicitly declaring all the dependencies required.

I am not aware of such good practice. Can you please reference me to Google documentation that defines it? If not, please provide another widely accepted guidance reference.

Thank you