Add `nginxGateway.name` in helm chart

[lucacome]

As a user of NGF's Helm Charts
I want to use a nginxGateway.name to configure the names of my deployments
So that I don't have to use nameOverride to override the entire name.

Acceptance

• The nginxGateway.name field is added and controls the name of the NGF deployment.
• Update tests to use nginxGateway.name instead of nameOverride.