fix: fix template names in ingress controller pdb

[dvarrazzo]

The PodDisruptionBudget refers to template that don't exist.

Test:

$ helm template test --set podDisruptionBudget.enabled=true --set deployment.replicas=3 charts/apisix-ingress-controller/  > /dev/null
Error: template: apisix-ingress-controller/templates/pdb.yaml:25:11: executing "apisix-ingress-controller/templates/pdb.yaml" at <include "apisix-ingress-controller.fullname" .>: error calling include: template: no template "apisix-ingress-controller.fullname" associated with template "gotpl"

Use --debug flag to render out invalid YAML

[dvarrazzo]

(IMO it would be better to clean up the helper name and remove the -manager bit everywhere).