Add ability to define templates library at module level

[pditommaso]

This PR replaces #2263 adding some minor refactoring and unit testing.

[manuelesimi]

I added a Module Templates section to the DSL2 doc.

I noticed how you tested the behavior of TaskContext with the new template location. Brilliant, congrats! I realize I didn't have enough knowledge of NF to write something like that.... For one, I was forgetting to enable DSL2 in my tests:)

[pditommaso]

Thinks looks great. Just made a comment on file template existence check.

[abhi18av]

I'm just curious here, the approach used in this PR , could also be applied for module level bin folder as well right ?

#1798

[manuelesimi]

@abhi18av The rational behind #1798 is indeed the same of this PR. They both aim to achieve self-contained module components. However, the solution found in this PR does not apply for the bin folder.
The templates dir is resolved locally, before the task is submitted to the execution layer. On the other hand, the bin dir must be uploaded on the node where the task is executed. Another difference is that there is only one template file per task, while multiple executable scripts can be both in the module's and workflow's bin folder.

That said, solving #1798 would nicely pair with the solution we got here.

[abhi18av]

On the other hand, the bin dir must be uploaded on the node where the task is executed.

Ah, I see!

Thanks for the detailed explanation @manuelesimi!

[pditommaso]

Ok, think we can merge this. Nice contribution @manuelesimi, thanks!

[manuelesimi]

Ok, think we can merge this. Nice contribution @manuelesimi, thanks!

You're welcome!