Added support to configure default vault namespace on the agent config

[flaviolemos78]

At the moment the only option to configure vault enterprise namespace is through the annotation vault.hashicorp.com/namespace at Pod level.
This presents some autonomy challenges for cluster/vault administrators. Example:

• When migrating to Vault enterprise namespaces, administrators aren't able to seamless change the injector vault until the last "workload" add the namespace annotation....

This PR adds the ability to define a default vault namespace on the agent config. If the vault namespace isn't defined at Pod, then the configured vault namespace will be used, otherwise the Pod annotation value is used

[tvoran]

Thanks! This is a nice addition, and tested great for me.

[flaviolemos78]

Hi @tvoran, do you know when will be the next release with this?

[bradfordwagner]

@flaviolemos78 - I'll follow this up with a MR against the helm chart.