Warn about config limits for scripts

[philderbeast]

Same as #6603 but cherry-picked over the stable branch.

[mpilgrem]

Closing, as duplicative of:

• the existing online documentation - see https://docs.haskellstack.org/en/stable/scripts/#stack-configuration-for-scripts and https://docs.haskellstack.org/en/stable/script_command/; and

• 6603.

The existing documentation for stack script and the Stack interpreter option comment already explain (at some length, contrasting with stack runghc) that:

• project-level configuration files are ignored and that this is a deliberate design choice; and
• global configuration is not ignored, and allow-newer etc is given as an express example.

If the underlying motivation is that the stack script command should have an --allow-newer flag, then please raise that as a separate issue.

[mpilgrem]

I have, however, attempted to make the existing language in the online documentation clearer and remove any ambiguity.