Add feature to hide specific volumes / bind mounts from size calculation

[zjean]

I am using a borgmatic container to backup my data to an external hard drive. This hard drive is mounted with a bind mount into the borgmatic container.
I would like to be able to exclude this directory from the doku views, since it gives a false view of the size of the data that is in use.
Are you open for a PR?

I would add an environment variable containing paths that should be excluded, and filter on them in app/bindmounts/size.go

[amerkurev]

Hello @zjean! Anyone who wants to contribute and make the project better is welcome to submit a PR. Your idea looks interesting and useful! I'd be happy to include it.