import: Set plan_type to SELF_HOSTED on import.
import: Set plan_type to SELF_HOSTED on import.

We've for a while had logic to set plan_type to LIMITED when importing
into Zulip Cloud; we need corresponding logic to set it to SELF_HOSTED
when importing into a self-hosted server.

Fixes #11541.

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