Replace console variables in spreadsheet header

In the campaign, the extra_rows contain the variables for branch,
target, and plan name. This commit makes host controller replace
the variables before uploading to spreadsheet.

Test: sheet --src= --dest= --client_secrets= --extra_rows={timestamp}
Bug: 79905934
Change-Id: I1dccafeb79cf2e28028d9f51fbe6aec55a73c043