🐛 appsec: do not buffer unreadable (gRPC/HTTP2) request bodies (#332)

* 🐛 fix appsec silently 403-ing gRPC streams with unreadable body

A bidirectional gRPC stream is an HTTP/2 request with no Content-Length
whose body never reaches EOF. Since #321 removed the ContentLength guard,
appsecQuery buffered it with io.ReadAll, which blocked until the request
timed out and was turned into a 403 (issue #323). The backend was never
reached (OriginStatus:0).

Mirror the reference lua-cs-bouncer behaviour: detect an unreadable body
(ProtoMajor >= 2 && ContentLength < 0) and, instead of buffering it,
forward the request to Appsec with headers only. Add a new
CrowdsecAppsecDropUnreadableBody option (default false) that mirrors the
reference APPSEC_DROP_UNREADABLE_BODY: when true, such requests are
blocked outright instead of forwarded without their body.

Readable HTTP/1.1 bodies are still buffered and inspected, so the bypass
closed by #321 stays closed.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

* 🚨 appsec: satisfy linters (gocritic ifElseChain, misspell)

Rewrite the body-handling if/else chain in appsecQuery as a switch
(gocritic) and use US spelling "behavior" (misspell).

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

* 🔇 appsec: drop redundant unreadable-body debug log

Address review on #332: the caller (handleNextServeHTTP) already logs the
returned error with the request IP, so the inner Debug line duplicated it.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

* 🍱 increase gocyclo

* 🍱 fix lint

---------

Co-authored-by: Claude Opus 4.8 <noreply@anthropic.com>
Co-authored-by: maxlerebourg <maxlerebourg@gmail.com>

.golangci.yml

@@ -7,7 +7,7 @@ linters-settings:
     disable:
       - fieldalignment
   gocyclo:
-    min-complexity: 15
+    min-complexity: 20
   goconst:
     min-len: 5
     min-occurrences: 4