templates: Extend templates/404.html to support a 405 error message.
templates: Extend templates/404.html to support a 405 error message.

Fixes: #16164.

rht/zulip,rht/zulip,zulip/zulip,hackerkid/zulip,hackerkid/zulip,punchagan/zulip,punchagan/zulip,andersk/zulip,hackerkid/zulip,zulip/zulip,punchagan/zulip,zulip/zulip,showell/zulip,eeshangarg/zulip,showell/zulip,showell/zulip,kou/zulip,hackerkid/zulip,zulip/zulip,rht/zulip,kou/zulip,eeshangarg/zulip,showell/zulip,showell/zulip,punchagan/zulip,rht/zulip,hackerkid/zulip,showell/zulip,andersk/zulip,kou/zulip,punchagan/zulip,eeshangarg/zulip,kou/zulip,kou/zulip,kou/zulip,andersk/zulip,andersk/zulip,eeshangarg/zulip,andersk/zulip,hackerkid/zulip,punchagan/zulip,andersk/zulip,hackerkid/zulip,zulip/zulip,rht/zulip,showell/zulip,eeshangarg/zulip,rht/zulip,andersk/zulip,eeshangarg/zulip,zulip/zulip,punchagan/zulip,zulip/zulip,eeshangarg/zulip,rht/zulip,kou/zulip