dfx new --frontend cli argument is wrong in the documentation

[testpuddle]

In: https://internetcomputer.org/docs/current/developer-docs/developer-tools/cli-tools/cli-reference/dfx-new#flags

The list of flags provided includes plain-assets.

The documentation should be changed to simple-assets to reflect the program as shown here:

dfx new --frontend --help [possible values: sveltekit, vanilla, vue, react, simple-assets, none]

[jessiemongeon1]

This documentation is maintained in the sdk repo. Moving this issue here.