streams: Enable live update of stream_post_policy in subscription_type text.
streams: Enable live update of stream_post_policy in subscription_type text.

This commits adds the code for live update of stream_post_policy in
subscription_type text in stream settings.

This is done by passing stream_data.stream_post_policy_values to the
template data, which were not passed previously and the if conditions
were not evaluated correctly.

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