[FEATURE] add config item to treat everything as symlink by default

[laur89]

Is your feature request related to a problem? Please describe.
No problem per se.

Describe the solution you'd like
I'd like an opt-in config item to treat every asset as symlink by default. For my use-case I don't see myself using the templating feature (but do see its value), and instead of verbosely defining certain files as symlinks in config to avoid the warnings at deploy time, I'd prefer dotter to treat everything as either symlink or template by default, but still allowing to explicitly override specific files.

Describe alternatives you've considered
No other alternative than to explicitly define warning-producing non-template files as symlinks.