feat: implement challenge registry (#607)

* feat: implement challenge method registry

This paves the way for implementing a no-js check method (#95) by making
the challenge providers more generic.

Signed-off-by: Xe Iaso <me@xeiaso.net>

* fix(lib/challenge): rename proof-of-work package to proofofwork

Signed-off-by: Xe Iaso <me@xeiaso.net>

* fix(lib): make validated challenges a CounterVec

Signed-off-by: Xe Iaso <me@xeiaso.net>

* fix(lib): annotate jwts with challenge method

Signed-off-by: Xe Iaso <me@xeiaso.net>

* test(lib/challenge/proofofwork): implement tests

Signed-off-by: Xe Iaso <me@xeiaso.net>

* test(lib): add smoke tests for known good and known bad config files

Signed-off-by: Xe Iaso <me@xeiaso.net>

* docs: update CHANGELOG

Signed-off-by: Xe Iaso <me@xeiaso.net>

* fix(lib): use challenge.Impl#Issue when issuing challenges

Signed-off-by: Xe Iaso <me@xeiaso.net>

---------

Signed-off-by: Xe Iaso <me@xeiaso.net>

lib/policy/config/config_test.go

@@ -130,20 +130,6 @@ func TestBotValid(t *testing.T) {
 			},
 			err: ErrChallengeDifficultyTooHigh,
 		},
-		{
-			name: "challenge wrong algorithm",
-			bot: BotConfig{
-				Name:      "mozilla-ua",
-				Action:    RuleChallenge,
-				PathRegex: p("Mozilla"),
-				Challenge: &ChallengeRules{
-					Difficulty: 420,
-					ReportAs:   4,
-					Algorithm:  "high quality rips",
-				},
-			},
-			err: ErrChallengeRuleHasWrongAlgorithm,
-		},
 		{
 			name: "invalid cidr range",
 			bot: BotConfig{
@@ -361,7 +347,7 @@ func TestBotConfigZero(t *testing.T) {
 	b.Challenge = &ChallengeRules{
 		Difficulty: 4,
 		ReportAs:   4,
-		Algorithm:  AlgorithmFast,
+		Algorithm:  DefaultAlgorithm,
 	}
 	if b.Zero() {
 		t.Error("BotConfig with challenge rules is zero value")