Make "--assembly_type" optional (change default to 'auto')

Description of features

Feature 1: (update: solved)

With https://github.com/nf-core/bacass/pull/270 it became possible to choose several assemblers. The default is however to use Unicycler only. Instead to actively opt-in to assemblers, I propose to rather opt-out if needed. That would mean by default all assembler are chosen (i.e. default of --assembler and --autocycler_assemblers is changed to all available options). That would mean the user will have to customize the params to get less assemblies (i.e. reduce output) instead of currently needing to specify when more tools should be used.

I guess here are two philosophies at play: Either activate all options by default, i.e. with default a large choice is offered, or activate based on pre-knowledge. I tend to offer all options by default, inspiring to compare tool outputs instead of just accepting the default outcome.

Feature 2: (update: still pending)

Additionally, it could be investigated whether it would be possible to make --assembly_type optional. By default, all available data would be used (new default: --assembly_type "auto"). That would mean that with both, short and long read data, long-read only & short read only & hybrid assemblers are all run. A hybrid assembler would always get both read types, if available. If only long reads are available, all options that can work with only long reads would be executed. Its the same idea as before: do and use what is possible by default, instead of restrict by default.

Any opinions?