docs: Add setting to conf.py to disable sticky_navigation
docs: Add setting to conf.py to disable sticky_navigation

The left navigation bar defaults to "sticking" to the screen as you
scroll.  This commit adds the sticky_navigation setting to conf.py to
disable the default behavior.

This addresses part of #5265.

kou/zulip,shubhamdhama/zulip,brainwane/zulip,synicalsyntax/zulip,jackrzhang/zulip,punchagan/zulip,synicalsyntax/zulip,punchagan/zulip,hackerkid/zulip,brainwane/zulip,rishig/zulip,shubhamdhama/zulip,tommyip/zulip,shubhamdhama/zulip,eeshangarg/zulip,dhcrzf/zulip,rishig/zulip,dhcrzf/zulip,brainwane/zulip,mahim97/zulip,hackerkid/zulip,andersk/zulip,hackerkid/zulip,tommyip/zulip,showell/zulip,synicalsyntax/zulip,shubhamdhama/zulip,kou/zulip,showell/zulip,zulip/zulip,jackrzhang/zulip,mahim97/zulip,andersk/zulip,dhcrzf/zulip,punchagan/zulip,punchagan/zulip,timabbott/zulip,rishig/zulip,rht/zulip,brainwane/zulip,andersk/zulip,rishig/zulip,shubhamdhama/zulip,brainwane/zulip,kou/zulip,tommyip/zulip,rht/zulip,eeshangarg/zulip,rishig/zulip,zulip/zulip,tommyip/zulip,timabbott/zulip,kou/zulip,rishig/zulip,jackrzhang/zulip,andersk/zulip,eeshangarg/zulip,jackrzhang/zulip,timabbott/zulip,rht/zulip,showell/zulip,zulip/zulip,brainwane/zulip,timabbott/zulip,rht/zulip,synicalsyntax/zulip,rht/zulip,synicalsyntax/zulip,tommyip/zulip,timabbott/zulip,jackrzhang/zulip,tommyip/zulip,andersk/zulip,showell/zulip,dhcrzf/zulip,zulip/zulip,rht/zulip,kou/zulip,rishig/zulip,kou/zulip,showell/zulip,andersk/zulip,punchagan/zulip,eeshangarg/zulip,kou/zulip,eeshangarg/zulip,shubhamdhama/zulip,andersk/zulip,hackerkid/zulip,mahim97/zulip,zulip/zulip,dhcrzf/zulip,timabbott/zulip,jackrzhang/zulip,hackerkid/zulip,punchagan/zulip,timabbott/zulip,zulip/zulip,showell/zulip,punchagan/zulip,mahim97/zulip,brainwane/zulip,eeshangarg/zulip,showell/zulip,jackrzhang/zulip,zulip/zulip,eeshangarg/zulip,dhcrzf/zulip,hackerkid/zulip,dhcrzf/zulip,rht/zulip,mahim97/zulip,hackerkid/zulip,shubhamdhama/zulip,synicalsyntax/zulip,synicalsyntax/zulip,mahim97/zulip,tommyip/zulip