Eliminate silent test skips in test/e2e/

[shreemaan-abhishek]

Audit all 11 Skip(...) sites in test/e2e/. For each: make it pass, gate on a documented environment flag, or remove the feature.

Specific known cases:

• skywalking (already landed via PR test: enable skywalking plugin in e2e apisix #32 / closes Follow-up: a6 test / skills / docs review findings #14 P0)
• ai-content-moderation
• stream-mode ssl-stream-route
• global-rule labels
• debug-logs auto-detect

Part of #33