update file_upload_v2 parameters

[Ximinhan]

fix error

UserWarning: Although the channels parameter is still supported for smooth migration from legacy files.upload, we recommend using the new channel parameter with a single str value instead for more clarity.
The filetype parameter is no longer supported. Please remove it from the arguments.

update channels parameter to channel
remove filetype parameter
file parameter should accept file path string
and file_upload_v2 will call files.completeUploadExternal which seems only accept channel_id so set channel with id instead of its name

[openshift-ci]

@Ximinhan: The following test failed, say /retest to rerun all failed tests or /retest-required to rerun all mandatory failed tests:

Test name	Commit	Details	Required	Rerun command
ci/prow/security	cec67b7	link	false	/test security

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[joepvd]

/lgtm

[openshift-ci]

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