Use default VS and TS templates when CfgMap obj is deleted

[jjngx]

Proposed changes

This PR introduces following change:

• NIC reverts to using default VS and TS templates after custom VS and TS templates (provided by config map obj) are deleted
• There is no need to restart the NIC pod to revert to custom templates

Test in kind:

VS config before applying custom template from configMap:

nginx@nginx-ingress-7fb4ff9677-z4t7b:/etc/nginx/conf.d$ head vs_default_cafe.conf

upstream vs_default_cafe_coffee {
    zone vs_default_cafe_coffee 512k;
    random two least_conn;
    server 10.244.0.6:8080 max_fails=1 fail_timeout=10s max_conns=0;
    server 10.244.0.7:8080 max_fails=1 fail_timeout=10s max_conns=0;

}
...

VS after applying custom template from configMap:

nginx@nginx-ingress-7fb4ff9677-z4t7b:/etc/nginx/conf.d$ head vs_default_cafe.conf
# ===============================================
# ==== VirtualServer TEMPLATE from ConfigMap ====
# ===============================================
#
# TEST!!!!
#
upstream vs_default_cafe_coffee {
    zone vs_default_cafe_coffee 512k;
    random two least_conn;
    server 10.244.0.6:8080 max_fails=1 fail_timeout=10s max_conns=
...

pod logs:

...

I20241111 14:12:39.372865   1 controller.go:262] Event(v1.ObjectReference{Kind:"ConfigMap", Namespace:"nginx-ingress", Name:"nginx-config", UID:"054001d6-4f81-43aa-b5b9-07a9d29fc8a3", APIVersion:"v1", ResourceVersion:"11892", FieldPath:""}): type: 'Normal' reason: 'Updated' Configuration from nginx-ingress/nginx-config was updated
I20241111 14:12:39.373038   1 controller.go:262] Event(v1.ObjectReference{Kind:"VirtualServer", Namespace:"default", Name:"cafe", UID:"edd41c17-e78e-40a4-9f86-c5b485f46963", APIVersion:"k8s.nginx.org/v1", ResourceVersion:"5989", FieldPath:""}): type: 'Normal' reason: 'AddedOrUpdated' Configuration for default/cafe was added or updated
2024/11/11 14:12:39 [notice] 127#127: exit
2024/11/11 14:12:39 [notice] 128#128: exit
2024/11/11 14:12:39 [notice] 22#22: signal 17 (SIGCHLD) received from 120
...

remove the custom VS template - original, default template is applied:

nginx@nginx-ingress-7fb4ff9677-z4t7b:/etc/nginx/conf.d$ head vs_default_cafe.conf

upstream vs_default_cafe_coffee {
    zone vs_default_cafe_coffee 512k;
    random two least_conn;
    server 10.244.0.6:8080 max_fails=1 fail_timeout=10s max_conns=0;
    server 10.244.0.7:8080 max_fails=1 fail_timeout=10s max_conns=0;

}
...

pod logs:

...
I20241111 14:14:21.563389   1 controller.go:262] Event(v1.ObjectReference{Kind:"ConfigMap", Namespace:"nginx-ingress", Name:"nginx-config", UID:"054001d6-4f81-43aa-b5b9-07a9d29fc8a3", APIVersion:"v1", ResourceVersion:"12039", FieldPath:""}): type: 'Normal' reason: 'Updated' Configuration from nginx-ingress/nginx-config was updated
I20241111 14:14:21.563577   1 controller.go:262] Event(v1.ObjectReference{Kind:"VirtualServer", Namespace:"default", Name:"cafe", UID:"edd41c17-e78e-40a4-9f86-c5b485f46963", APIVersion:"k8s.nginx.org/v1", ResourceVersion:"5989", FieldPath:""}): type: 'Normal' reason: 'AddedOrUpdated' Configuration for default/cafe was added or updated
2024/11/11 14:14:21 [notice] 137#137: exit
...

Checklist

Before creating a PR, run through this checklist and mark each as complete.

• [X] I have read the CONTRIBUTING doc
• [X] I have added tests that prove my fix is effective or that my feature works
• [X] I have checked that all unit tests pass after adding my changes
• [ ] I have updated necessary documentation
• [X] I have rebased my branch onto main
• [X] I will ensure my PR is targeting the main branch and pulling from my branch from my own fork

[codecov[bot]]

Codecov Report

Attention: Patch coverage is 68.57143% with 11 lines in your changes missing coverage. Please review.

Project coverage is 53.46%. Comparing base (64de3b8) to head (5ef4d7a). Report is 1 commits behind head on main.

Files with missing lines	Patch %	Lines
internal/configs/version2/template_executor.go	57.14%	6 Missing and 3 partials :warning:
internal/configs/configmaps.go	50.00%	0 Missing and 2 partials :warning:

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #6780 +/- ## ========================================== + Coverage 53.38% 53.46% +0.07% ========================================== Files 89 89 Lines 20195 20218 +23 ========================================== + Hits 10781 10809 +28 + Misses 8977 8965 -12 - Partials 437 444 +7 ```

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