document regexes support in filtering options

[sigilioso]

Is your feature request related to a problem? Please describe. I'd like the collection filtering possibilities to be described in --mongodb.collstats-colls and --mongodb.indexstats-colls options documentation.

Describe the solution you'd like Considering the listsCollections documentation regexes are supported in collection names, however if we check the reference or the readme docs, it doesn't seem that regexes are supported.

Unless this behavior could change in the future and omitting it in the docs is intentional, I think that including the regexes support in the docs would be useful.

Describe alternatives you've considered

Additional context