EXAMPLES: add a "basic-config-edge" example config

This config uses TLS, HSTS, redirects, cache, compression, stats,
log to stderr, and simple load balancing in a simple and commented
config which could be used as a starter for many other ones,
especially in containers.

examples/basic-config-edge.cfg

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+# This configuration creates a classical reverse-proxy and load balancer for
+# public services. It presents ports 80 and 443 (with 80 redirecting to 443),
+# enables caching up to one hour, and load-balances the service on a farm of
+# 4 servers on private IP addresses which are checked using HTTP checks and
+# by maintaining stickiness via session cookies. It offloads TLS processing
+# and enables HTTP compression. It uses HAProxy 2.4.
+
+# The global section deals with process-wide settings (security, resource usage)
+global
+	# all file names are relative to the directory containing this config
+	# file by default
+	default-path config
+
+	# refuse to start if any warning is emitted at boot (keep configs clean)
+	zero-warning
+
+	# Security hardening: isolate and drop privileges
+	chroot /var/empty
+	user haproxy
+	group haproxy
+
+	# daemonize
+	daemon
+	pidfile /var/run/haproxy-svc1.pid
+
+	# do not keep old processes longer than that after a reload
+	hard-stop-after 5m
+
+	# The command-line-interface (CLI) used by the admin, by provisionning
+	# tools, and to transfer sockets during reloads
+	stats socket /var/run/haproxy-svc1.sock level admin mode 600 user haproxy expose-fd listeners
+	stats timeout 1h
+
+	# send logs to stderr for logging via the service manager
+	log stderr local0 info
+
+	# intermediate security for SSL, from https://ssl-config.mozilla.org/
+	ssl-default-bind-ciphers ECDHE-ECDSA-AES128-GCM-SHA256:ECDHE-RSA-AES128-GCM-SHA256:ECDHE-ECDSA-AES256-GCM-SHA384:ECDHE-RSA-AES256-GCM-SHA384:ECDHE-ECDSA-CHACHA20-POLY1305:ECDHE-RSA-CHACHA20-POLY1305:DHE-RSA-AES128-GCM-SHA256:DHE-RSA-AES256-GCM-SHA384
+	ssl-default-bind-ciphersuites TLS_AES_128_GCM_SHA256:TLS_AES_256_GCM_SHA384:TLS_CHACHA20_POLY1305_SHA256
+	ssl-default-bind-options prefer-client-ciphers no-sslv3 no-tlsv10 no-tlsv11 no-tls-tickets
+
+# default settings common to all HTTP proxies below
+defaults http
+	mode http
+	option httplog
+	log global
+	timeout client 1m
+	timeout server 1m
+	timeout connect 10s
+	timeout http-keep-alive 2m
+	timeout queue 15s
+	timeout tunnel 4h  # for websocket
+
+# provide a stats page on port 8181
+frontend stats
+	bind :8181
+	# provide advanced stats (ssl, h2, ...)
+	stats uri /
+	stats show-modules
+	# some users may want to protect the access to their stats and/or to
+	# enable admin mode on the page from local networks
+	#  stats auth admin:mystats
+	#  stats admin if { src 10.0.0.0/8 172.16.0.0/12 192.168.0.0/16 127.0.0.0/8 }
+
+# First incoming public service. Supports HTTP/1.x and HTTP/2, using HSTS,
+# redirects clear to TLS. Uses a dedicated host name for the stats page.
+frontend pub1
+	bind :80 name clear
+	bind :443 name secure ssl crt pub1.pem alpn h2,http/1.1
+	option socket-stats  # provide per-bind line stats
+
+	# set HSTS for one year after all responses
+	http-after-response set-header Strict-Transport-Security "max-age=31536000"
+	http-request redirect scheme https code 301 if !{ ssl_fc }
+
+	# silently ignore connect probes and pre-connect without request
+	option http-ignore-probes
+
+	# pass client's IP address to the server and prevent against attempts
+	# to inject bad contents
+	http-request del-header x-forwarded-for
+	option forwardfor
+
+	# enable HTTP compression of text contents
+	compression algo deflate gzip
+	compression type text/ application/javascript application/xhtml+xml image/x-icon
+
+	# enable HTTP caching of any cacheable content
+        http-request  cache-use cache
+        http-response cache-store cache
+
+	default_backend app1
+
+# The cache instance used by the frontend (200MB, 10MB max object, 1 hour max)
+# May be consulted using "show cache" on the CLI socket
+cache cache
+	total-max-size 200        # RAM cache size in megabytes
+	max-object-size 10485760  # max cacheable object size in bytes
+	max-age 3600              # max cache duration in seconds
+	process-vary on           # handle the Vary header (otherwise don't cache)
+
+# First application
+backend app1
+	# Algorithm:
+	#  - roundrobin is usually better for short requests,
+	#  - leastconn is better for mixed slow ones, and long transfers,
+	#  - random is generally good when using multiple load balancers
+	balance random
+
+	# abort if the client clicks on stop.
+	option abortonclose
+
+	# insert a session cookie for user stickiness
+	cookie app1 insert indirect nocache
+
+	# check the servers' health using HTTP requests
+	option httpchk
+	http-check send meth GET uri / ver HTTP/1.1 hdr host svc1.example.com
+
+	# do not overload the servers (100 concurrent conns max each)
+	server srv1 192.0.2.1:80 cookie s1 maxconn 100 check inter 1s
+	server srv2 192.0.2.2:80 cookie s2 maxconn 100 check inter 1s
+	server srv3 192.0.2.3:80 cookie s3 maxconn 100 check inter 1s
+	server srv4 192.0.2.4:80 cookie s4 maxconn 100 check inter 1s