chore: fix wasm file cache directory permission

[zhaohuabing]

This PR makes /var/lib/eg writable for any user. This allows the EG process to write Wasm cache into this directory when the UID has been changed by the Pod/Container SecurityContext.

Fixes: #5819 (comment)

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 70.48%. Comparing base (82ae1de) to head (8df558d).
Report is 6 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #6173   +/-   ##
=======================================
  Coverage   70.47%   70.48%           
=======================================
  Files         220      220           
  Lines       36625    36625           
=======================================
+ Hits        25811    25814    +3     
+ Misses       9284     9283    -1     
+ Partials     1530     1528    -2     

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[arkodg]

LGTM thanks !

[zhaohuabing]

0660/0770 won't work because

• execution permission is required to create files.
• other users(65532 or anyone specified in the SeucrityContex) require permissions to create files.

ControllerName:gateway.envoyproxy.io/gatewayclass-controller Conditions:[{Type:Accepted Status:False 
ObservedGeneration:1 LastTransitionTime:2025-05-28 10:30:32 +0000 UTC Reason:Invalid Message:Wasm: mkdir 
/var/lib/eg/wasm/65194423a990667b2db1fab45eb98890f1c47f802752b8a740dde075f966700a: permission denied.}]}]}}

[zhaohuabing]

This happens because the Envoy Gateway may lose the deletion message of Gateways while rollout restart, and the left Envoy proxies cause failure of the upgrade test.

This is an edge case found in this test - should EG proactively delete the Envoy proxies that are orphaned after Gateways are removed?

Manually delete the Envoy proxies after the test.

Related issue: #3051

https://github.com/envoyproxy/gateway/actions/runs/15431221218/job/43429760632?pr=6173

➜  gateway git:(fix-cache-permission) ✗ k -n envoy-gateway-system get pod -w
NAME                                                              READY   STATUS    RESTARTS   AGE
envoy-gateway-79df56475-946vz                                     1/1     Running   0          29s
envoy-gateway-conformance-infra-all-namespaces-302def45-5dj9bxt   1/2     Running   0          42s
envoy-gateway-conformance-infra-same-namespace-9baff503-69cchq4   1/2     Running   0          42s

[arkodg]

LGTM, thanks for adding the e2e