add license check to linter

Is your feature request related to a problem? Please describe

as part of software best practices, it's probably wise (and sometimes maybe necessary) to include software licenses for packaged software. for nf-core/modules, this would mean enforcing or at least noting the software license in meta.yml

Describe the solution you'd like

1. add code to the nf-core linter to check for a line in meta.yml such as license: ['MIT']
2. ensure that nf-core modules create also generates this line when templating a new module

Describe alternatives you've considered

could opt for no-build option, if people are happy with status quo. for those in environments with high audit risk, this could yield a rather painful experience down the road..

Additional context

see parallel issue in nf-core/modules here

Start by locating the nf-core linter implementation and the nf-core modules create template entry point. Check how meta.yml fields are currently validated and generated, then define the expected license format and verify both requested behaviors with the project's existing checks.