billing: Add default value for event_time in invoice_plans_as_needed.
billing: Add default value for event_time in invoice_plans_as_needed.

rishig/zulip,shubhamdhama/zulip,hackerkid/zulip,rht/zulip,showell/zulip,zulip/zulip,rht/zulip,tommyip/zulip,kou/zulip,zulip/zulip,brainwane/zulip,kou/zulip,andersk/zulip,kou/zulip,shubhamdhama/zulip,andersk/zulip,hackerkid/zulip,rht/zulip,punchagan/zulip,timabbott/zulip,showell/zulip,andersk/zulip,andersk/zulip,showell/zulip,zulip/zulip,brainwane/zulip,eeshangarg/zulip,timabbott/zulip,brainwane/zulip,tommyip/zulip,shubhamdhama/zulip,synicalsyntax/zulip,brainwane/zulip,rishig/zulip,shubhamdhama/zulip,tommyip/zulip,synicalsyntax/zulip,timabbott/zulip,zulip/zulip,hackerkid/zulip,punchagan/zulip,eeshangarg/zulip,andersk/zulip,rht/zulip,synicalsyntax/zulip,rishig/zulip,timabbott/zulip,punchagan/zulip,hackerkid/zulip,tommyip/zulip,eeshangarg/zulip,punchagan/zulip,kou/zulip,rht/zulip,kou/zulip,synicalsyntax/zulip,showell/zulip,brainwane/zulip,brainwane/zulip,timabbott/zulip,rishig/zulip,kou/zulip,eeshangarg/zulip,rht/zulip,shubhamdhama/zulip,andersk/zulip,shubhamdhama/zulip,hackerkid/zulip,synicalsyntax/zulip,zulip/zulip,eeshangarg/zulip,timabbott/zulip,zulip/zulip,andersk/zulip,shubhamdhama/zulip,rishig/zulip,tommyip/zulip,brainwane/zulip,hackerkid/zulip,synicalsyntax/zulip,showell/zulip,tommyip/zulip,kou/zulip,timabbott/zulip,hackerkid/zulip,eeshangarg/zulip,zulip/zulip,rishig/zulip,punchagan/zulip,rishig/zulip,rht/zulip,showell/zulip,showell/zulip,punchagan/zulip,tommyip/zulip,eeshangarg/zulip,synicalsyntax/zulip,punchagan/zulip