Use the default http config for all server UI and rapi operations + Indicate when the UI/echo server is using https

[ldemailly]

Fixes #865 by introducing DefaultHTTPOptions and copies of it after it's set by the main()

Also:

go run . server -key ./cert-tmp/server.key -cert ./cert-tmp/server.crt 
[...]
12:22:37.835 r1 Using server cert and key from ./cert-tmp/server.crt and ./cert-tmp/server.key to construct TLS credentials
12:22:37.835 r1 Fortio dev https redirector server listening on tcp [::]:8081
12:22:37.835 r1 Fortio dev https-echo server listening on tcp [::]:8080
12:22:37.845 r1 Data directory is /Users/ldemailly/dev/fortio.org/fortio
12:22:37.845 r1 REST API on /fortio/rest/run, /fortio/rest/status, /fortio/rest/stop, /fortio/rest/dns
12:22:37.845 r1 Debug endpoint on /debug, Additional Echo on /debug/echo/, Flags on /fortio/flags, and Metrics on /debug/metrics
	 UI started - visit:
		https://localhost:8080/fortio/
	 (or any host/ip reachable on this server)

used to say http://localhost:8080/ for that case

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Comparison is base (80eca80) 88.5% compared to head (5906e7c) 88.6%.

Additional details and impacted files

@@          Coverage Diff           @@
##           master    #868   +/-   ##
======================================
  Coverage    88.5%   88.6%           
======================================
  Files          17      17           
  Lines        5011    5014    +3     
======================================
+ Hits         4437    4440    +3     
  Misses        424     424           
  Partials      150     150           

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