Rename discriminator to waf everywhere (closes #312)

The command is now `sww waf`, and the package is `internal/waf`. Types,
functions, files, tests, comments, docs, the Dockerfile, the runit
script, `script/`, compose examples, the log field `waf_line` and the
`X-From-Waf` test header follow. No behaviour changes, and no setting
changes name: rproxy already finds the waf through `SWRP_WAF_BACKEND`.

Done with one `sed -i` (Discriminator and DISCRIMINATOR to WAF,
discriminator to waf) over the files `git grep -i discriminator`
listed, as sneak allowed for this rename, then `git mv` for the
package and files. By hand afterwards: the header's spelling, which
the linter requires, and the padding after `waf` in `sww`'s usage
text.

Model: opus-5-5

internal/sww/healthcheck.go

@@ -11,7 +11,7 @@ import (
 	"time"
 
 	"sneak.berlin/go/smallwebwaf/internal/config"
-	"sneak.berlin/go/smallwebwaf/internal/discriminator"
+	"sneak.berlin/go/smallwebwaf/internal/waf"
 )
 
 // healthCheckTimeout bounds the whole health check.
@@ -19,8 +19,8 @@ const healthCheckTimeout = 5 * time.Second
 
 var errHealthEndpoint = errors.New("the health endpoint answered")
 
-// HealthCheck is the container's health check. In discriminator's container, where
-// SWW_COMMAND is discriminator, it returns 0 while discriminator answers its health
+// HealthCheck is the container's health check. In waf's container, where
+// SWW_COMMAND is waf, it returns 0 while waf answers its health
 // endpoint on 127.0.0.1, at the port in SWW_LISTEN_ADDR. In rproxy's container,
 // where SWW_COMMAND is rproxy, unset or empty, it returns 0 while rproxy
 // answers its health endpoint on 127.0.0.1, at the port in SWRP_LISTEN_ADDR, and
@@ -49,8 +49,8 @@ func HealthCheck(
 	switch {
 	case err != nil:
 		err = fmt.Errorf("invalid setting: %w", err)
-	case command == "discriminator":
-		err = checkDiscriminator(ctx, lookupEnv)
+	case command == "waf":
+		err = checkWAF(ctx, lookupEnv)
 	default:
 		err = checkRProxyAndApp(ctx, lookupEnv)
 	}
@@ -64,18 +64,18 @@ func HealthCheck(
 	return 0
 }
 
-// checkDiscriminator asks discriminator's health endpoint.
-func checkDiscriminator(
+// checkWAF asks waf's health endpoint.
+func checkWAF(
 	ctx context.Context, lookupEnv func(string) (string, bool),
 ) error {
-	listenAddr, err := config.DiscriminatorListenAddr(lookupEnv)
+	listenAddr, err := config.WAFListenAddr(lookupEnv)
 	if err != nil {
 		return fmt.Errorf("invalid setting: %w", err)
 	}
 
 	err = askHealthEndpoint(ctx, listenAddr)
 	if err != nil {
-		return fmt.Errorf("ask discriminator: %w", err)
+		return fmt.Errorf("ask waf: %w", err)
 	}
 
 	return nil
@@ -109,7 +109,7 @@ func checkRProxyAndApp(
 // listenAddr, which the settings have checked has one.
 func askHealthEndpoint(ctx context.Context, listenAddr string) error {
 	_, port, _ := net.SplitHostPort(listenAddr)
-	health := "http://" + net.JoinHostPort("127.0.0.1", port) + discriminator.HealthPath
+	health := "http://" + net.JoinHostPort("127.0.0.1", port) + waf.HealthPath
 
 	req, err := http.NewRequestWithContext(ctx, http.MethodGet, health, http.NoBody)
 	if err != nil {