Use secrets.stencil.json rather than creating a new access token file

[joeyhoer]

This setting could perhaps be optional. It seems redundant to add an accessToken to each widget configuration when one is already present in the theme secrets.stencil.json file.

This issue may be specific to how we organize themes. We typically store widget code in a widgets directory within the stencil theme.

theme/
└── widgets/
    └── widget/

If such a directory structure is used, then that accessToken can be used for all widgets.

Perhaps a separate, though related, feature suggestion is to add the apiPath value to the config.stencil.json file rather than adding that to another file.