[feature request] Add an option to hide parameters of digdag.env.store from web ui

[sonots]

My final purpose is to use secrets in embulk liquid files and in docker containers. If my final purpose can be achieved, another approach is acceptable for me.

To use secrets in embulk liquids or in docker containers, I currently need to map all secrets to environment variables. We can use digdag.env.store with python API to do it.

I wrote details at https://qiita.com/sonots/items/cb71834857235f965225 (Japanese)

For this purpose, I feel good if following is supported.

1. Add a python API to get secrets (so that I do not need to write _env) ref. https://github.com/treasure-data/digdag/issues/942
2. Add an option to digdag.env.store to hide from web ui of the digdag server. (this feature request)