feat: add e2e test suite with Robot Framework

Add e2e/ dir with Robot Framework tests for page loading, ban records,
blocklist import, config edit. Add requirements.txt. Update Makefile with
test commands. Update .gitignore, backend docs, testing requirements docs.

e2e/tests/03_blocklist_import.robot

@@ -0,0 +1,15 @@
+*** Settings ***
+Resource    ${CURDIR}/../../resources/common.resource
+Resource    ${CURDIR}/../../resources/auth.resource
+
+*** Test Cases ***
+Blocklist Import Page Opens
+    New Browser    chromium    headless=${TRUE}
+    Login As Admin
+
+    Go To    ${FRONTEND_URL}/blocklists
+
+    ${content}=    Get Page Source
+    Should Not Be Empty    ${content}
+
+    Close Browser