docs: split/link ext.args into user and developer sections (docs-v2)

[jfy133]

Currently the ext.args info sits in developer docs, which to a certain extent makes sense, as it's normally used for developers to input command line parameters into a process.

However in some cases a user may want to override these in a configuration file (even if this is not recommended!).

We should either spltuthe page into two for developers vs users, or (I think my preferred solution), link the page also into Running / Configuration but with a big warning that a user overriding pipeline ext.args defaults 'comes with no warranty nor support'.

[jfy133]

As per: https://nfcore.slack.com/archives/C09H9L3R614/p1774021312865689

[christopher-hakkaart]

Considerations:

• Applies to users who want to modify, developers who want to configure, and contributors who need to designed parameters and configs.
• We want to avoid duplications, but should look for ways to balance as findability and clicking across x pages is a pain point
• Also applied to meta