Add content-type to support protobuf for runkperf

[anson627]

This pull request introduces a new content-type flag to specify the content type (either JSON or Protocol Buffers) and updates the load profile generation to include this content type. The most important changes are summarized below:

New Feature Addition:

• contrib/cmd/runkperf/commands/bench/root.go: Added a new content-type flag to the commonFlags array to allow users to specify the content type as either JSON or Protocol Buffers. ([contrib/cmd/runkperf/commands/bench/root.goR83-R87](https://github.com/Azure/kperf/pull/133/files#diff-fbb70fa148e5f27e9fdf3e41d16d936d23670184a4e0bd5792fed70eb56fb036R83-R87))

Load Profile Update:

• contrib/cmd/runkperf/commands/bench/utils.go: Updated the newLoadProfileFromEmbed function to set the ContentType field in the load profile specification based on the new content-type flag. ([contrib/cmd/runkperf/commands/bench/utils.goL147-R147](https://github.com/Azure/kperf/pull/133/files#diff-0ecb63839ef4aa98fe23783072cffdf675738d1df358e0e5251cbe287b43e474L147-R147))

[anson627]

tested manually

I1028 21:56:46.931079  383475 utils.go:149] "Load Profile" config=<
        count: 1
        loadProfile:
          version: 1
          description: node10-job1-pod100
          spec:
            rate: 10
            total: 100
            conns: 10
            client: 10
            contentType: protobuf
            disableHTTP2: false
            maxRetries: 0
            requests:
            - shares: 1000
              staleList:
                group: ""
                version: v1
                resource: pods
                namespace: ""
                limit: 0
                seletor: ""
                fieldSelector: ""
            - shares: 100
              quorumList:
                group: ""
                version: v1
                resource: pods
                namespace: ""
                limit: 1000
                seletor: ""
                fieldSelector: ""
            - shares: 100
              quorumList:
                group: ""
                version: v1
                resource: events
                namespace: ""
                limit: 1000
                seletor: ""
                fieldSelector: ""
        nodeAffinity:
          node.kubernetes.io/instance-type:
          - Standard_D16s_v3
          - m4.4xlarge
          -