GCP Batch executor not including C4A machineType

[rhassaine]

Bug report

The machineType directive is not honored (this issue) - and the c4a machines are not included in the plugin code.
This, in turn, causes the c4a (arm-instances) to not be used either.
An issue has already been made about the machineType directive but not for updating the nf-google plugin code. Currently, when explicitly stated in the config, the jobs default back to n2 instances.

Expected behavior and actual behavior

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Steps to reproduce the problem

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Program output

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Environment

• Nextflow version: [?]
• Java version: [?]
• Operating system: [macOS, Linux, etc]
• Bash version: (use the command $SHELL --version)

Additional context

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