Enable use of shared `deny.toml`

[S-Coyle]

Is your feature request related to a problem? Please describe.
From what I can see, if I add this action to multiple crates I don't seem to be able to have a shared deny.toml which they can all point to. This means any updates would need to be made to each individual deny.toml

Describe the solution you'd like
The ability to point each crate to a shared deny.toml in an arbitrary location, therefore when I want to update the deny.toml I only need to do so in 1 single location and changes take effect across my crates.

Describe alternatives you've considered
I intend to try adding a wget of a shared deny.toml which will run immediately before the action

Additional context

[tgross35]

I think this would probably be helped by EmbarkStudios/cargo-deny#619