generate_zulip_bots_static_files: Lazy import cairosvg.
generate_zulip_bots_static_files: Lazy import cairosvg.

Importing cairosvg in fails in production, because `libgtk-3-dev` is not
available. This commit moves the import for `cairosvg` into the function
where it is used. This code will soon be moved into a separate script that
will not be run on production.

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