Added option for Parallel upload with grpc client

[jruszo]

Ticket:
https://perconadev.atlassian.net/browse/PBM-1776

Description:
Added optional configuration for ParallelUpload
Since it is experimental in the SDK according to Google, it is gated with "enable: true"

If the parallel upload is enabled, the client is also switched to the grpc version as per requirements.

Documentation is not updated, if pull request looks good, will submit for documentation as well

Example configuration snippet:

 Config shape:

  storage:
    gcs:
      parallelUpload:
        enabled: true
        partSize: 16777216 # Optional, default: 16MiB
        maxConcurrency: 4 # Optional, default: (min(4 + NumCPU/2, 16))

[it-percona-cla]

All committers have signed the CLA.

[boris-ilijic]

Hi @jruszo, thank you for your PR and jira ticket also. We'll soon discuss this improvement and come back to you asap.

[boris-ilijic]

Hey there! We're planning to include this feature in PBM v2.16. We'll review and look to merge your PR once development on that release kicks off. Thanks again for your contribution.

[jcechace]

@jruszo Thanks for the contribution. FYI I have picked it up under #1344

Few things that came up when reviewing

• IMHO it's better to have explicit clientType field that switches between json and grpc, rather than hidden switch
• grpc client definitively needs to be closed, so that's what I am currently working on.

We would like to include it in the next release as an experimental feature, but need to solve the closing issue first.

[jcechace]

Will be followed up by #1344