integrations: Specify a generic URL in GithubIntegration.
integrations: Specify a generic URL in GithubIntegration.

We now supply a generic URL for our legacy and webhook GitHub
integrations, as opposed to a dynamically generated URLs
for all other WebhookIntegration(s). Previously, within
GithubIntegration, an invalid URL was dynamically generated
which wasn't even used. Now, we just manually supply the URL
to GithubIntegration.

Furthermore, we'll now be able to access the correct URL in
`render_markdown_path` for our macros.

rishig/zulip,vabs22/zulip,eeshangarg/zulip,Galexrt/zulip,vabs22/zulip,kou/zulip,timabbott/zulip,timabbott/zulip,verma-varsha/zulip,andersk/zulip,verma-varsha/zulip,punchagan/zulip,brockwhittaker/zulip,amanharitsh123/zulip,jrowan/zulip,dhcrzf/zulip,tommyip/zulip,brainwane/zulip,punchagan/zulip,jackrzhang/zulip,rht/zulip,amanharitsh123/zulip,verma-varsha/zulip,showell/zulip,punchagan/zulip,synicalsyntax/zulip,tommyip/zulip,Galexrt/zulip,zulip/zulip,rishig/zulip,jackrzhang/zulip,dhcrzf/zulip,jackrzhang/zulip,shubhamdhama/zulip,brockwhittaker/zulip,rishig/zulip,jrowan/zulip,jrowan/zulip,rht/zulip,vabs22/zulip,vaidap/zulip,vaidap/zulip,brockwhittaker/zulip,hackerkid/zulip,kou/zulip,andersk/zulip,punchagan/zulip,brainwane/zulip,showell/zulip,amanharitsh123/zulip,zulip/zulip,rishig/zulip,shubhamdhama/zulip,synicalsyntax/zulip,dhcrzf/zulip,dhcrzf/zulip,eeshangarg/zulip,punchagan/zulip,shubhamdhama/zulip,timabbott/zulip,hackerkid/zulip,kou/zulip,verma-varsha/zulip,shubhamdhama/zulip,rht/zulip,vabs22/zulip,andersk/zulip,brainwane/zulip,shubhamdhama/zulip,Galexrt/zulip,rht/zulip,timabbott/zulip,mahim97/zulip,timabbott/zulip,eeshangarg/zulip,showell/zulip,brainwane/zulip,vaidap/zulip,hackerkid/zulip,zulip/zulip,hackerkid/zulip,amanharitsh123/zulip,dhcrzf/zulip,brainwane/zulip,eeshangarg/zulip,amanharitsh123/zulip,kou/zulip,tommyip/zulip,vabs22/zulip,punchagan/zulip,rht/zulip,synicalsyntax/zulip,andersk/zulip,jackrzhang/zulip,tommyip/zulip,verma-varsha/zulip,zulip/zulip,vaidap/zulip,hackerkid/zulip,kou/zulip,showell/zulip,mahim97/zulip,shubhamdhama/zulip,showell/zulip,synicalsyntax/zulip,rishig/zulip,timabbott/zulip,rishig/zulip,Galexrt/zulip,jrowan/zulip,eeshangarg/zulip,vaidap/zulip,hackerkid/zulip,brockwhittaker/zulip,showell/zulip,andersk/zulip,andersk/zulip,tommyip/zulip,zulip/zulip,jackrzhang/zulip,mahim97/zulip,jackrzhang/zulip,kou/zulip,brockwhittaker/zulip,showell/zulip,punchagan/zulip,vabs22/zulip,jackrzhang/zulip,brainwane/zulip,mahim97/zulip,tommyip/zulip,synicalsyntax/zulip,Galexrt/zulip,mahim97/zulip,tommyip/zulip,synicalsyntax/zulip,kou/zulip,eeshangarg/zulip,dhcrzf/zulip,brainwane/zulip,zulip/zulip,brockwhittaker/zulip,hackerkid/zulip,synicalsyntax/zulip,shubhamdhama/zulip,rht/zulip,rishig/zulip,dhcrzf/zulip,amanharitsh123/zulip,Galexrt/zulip,mahim97/zulip,jrowan/zulip,jrowan/zulip,verma-varsha/zulip,zulip/zulip,Galexrt/zulip,timabbott/zulip,rht/zulip,andersk/zulip,eeshangarg/zulip,vaidap/zulip