Caddy telemetry: a global, server-side perspective of the health of the Internet

Also improve handling of disabled metrics, and record TLS ClientHello
in association with User-Agent

# Conflicts:
#	caddy/caddymain/run.go
#	caddyhttp/httpserver/plugin.go
#	caddytls/client.go

* Enabled configurable Timeout for the proxy directive

* Added Test for reverse for proxy timeout

* Removed Duplication in proxy constructors

* Remove indirection from multiple constructors and refactor into one

* Fix inconsistent error message and refactor dialer initialization

* Regexp support for simple rewrite rule

* Add negate option for simplicity

* ascertain explicit regexp char

* Fixes #1960 Transparent proxy not appending
existing X-Forwarded-For header

* Fixes #1960 Formatting Code

* caddyfile: More robust parsing for 'import' (fixes #2096)

The fix for hanging involves limiting the number of wildcards in an
import pattern to just 1. Otherwise some patterns can expand to the
entire disk.

The other fix requires that the end string for an environment variable
expansion come after the start string.

* caddyfile: Fix more fuzzing errors

- Introduce StrictHostMatching mode for sites that require clientauth
- Error if QUIC is enabled whilst TLS clientauth is configured
  (Our QUIC implementation does not yet support TLS clientauth, but
  maybe it will in the future - fixes #2095)
- Error if one but not all TLS configs for the same hostname have a
  different ClientAuth CA pool

Apparently Cloudflare just caused 1.1.1.1 to resolve, so we have to
change our test IP, hopefully this is better

* proof of concept

* Initial implementation with debug code

* Tidy up debug code

* remove unneeded import

* removed extra line

* Move ShouldLog function to rule entry Logger type

* add tests for ShouldLog

* Added tests for log exceptions

* Fix logic

* fix govet fail for test

* Updates requested for code clarity

* Update requested for style

* log: Minor style tweaks to logic of log exceptions

tls: Use ACMEv2 and support automatic wildcard certificates

# Conflicts:
#	caddyhttp/httpserver/replacer.go
#	caddyhttp/httpserver/replacer_test.go

* different cases in path make different keys

* Respect CaseSensitivePath variable when matching paths

Also fix a couple metrics that were named wrong or reported in excess.

An attempt to future-proof older Caddy instances so that they won't
keep trying to send telemetry to endpoints that just simply aren't
going to be available

* httpserver.Replacer: Rework loop to ignore escaped placeholder braces

* Fix typo and ineffectual assignment to ret

* Remove redundant idxOffset declaration, simplify escape check

* Add benchmark tests for new Replacer code

Improve error message and backoff as well