gopass: Make NAMESPACE customizable

[stefanmore]

Hi,
First of all, thank you for all your efforts in creating the gopass helper / this fork!

Context:

I noticed that currently NAMESPACE is hardcoded to io.container.registries, i.e., passwords are stored in ~/.password-store/io.container.registries.

For some reason, another machine I used to use put passwords into the docker-credential-helpers namespace. Unfortunately, I cannot remember which helper I used at the time.

Feature Proposal:

Thus, I propose to allow the customization of NAMESPACE, e.g., via ~/.docker/config.json.

Obviously, there are workarounds (such as moving the old passwords or modifying the variable before compiling). So this is not a high-proprity PR.

[stefanmore]

I just noticed that the pass helper uses the docker-credential-helpers string:

docker-credential-helpers/pass/pass.go

Line 24 in 9082d90

const PASS_FOLDER = "docker-credential-helpers" //nolint:revive

Perhaps I used a wrapper around 'pass' in the past ...