tests-httpd: basic infra to run curl against an apache httpd plus nghttpx for h3

- adding '--with-test-httpd=<path>' to configure non-standard apache2
  install
- python env and base classes for running httpd
- basic tests for connectivity with h1/h2/h3
- adding test cases for truncated responses in http versions.
- adding goaway test for HTTP/3.
- adding "stuttering" tests with parallel downloads in chunks with
  varying delays between chunks.

- adding a curltest module to the httpd server, adding GOAWAY test.
    - mod_curltest now installs 2 handlers
      - 'echo': writing as response body what came as request body
      - 'tweak': with query parameters to tweak response behaviour
- marked known fails as skip for now

Closes #10175

.github/scripts/spellcheck.words

@@ -20,6 +20,8 @@ AmigaOS
 AmiSSL
 anyauth
 anycast
+apache
+Apache
 API
 APIs
 APOP
@@ -135,6 +137,7 @@ CURLE
 CURLH
 curlimages
 curlrc
+curltest
 customizable
 CVE
 CVSS
@@ -295,6 +298,8 @@ hsts
 HTC
 html
 http
+httpd
+HTTPD
 HTTPAUTH
 httpget
 HttpGet
@@ -577,6 +582,8 @@ ptr
 punycode
 py
 pycurl
+pytest
+Pytest
 QNX
 QoS
 Qubes