Give file_pretrained_model an example

[rcannood]

viash test currently fails for every *_train component on main:

>> Running test 'run'
>> Running the component executable
[error] --output is a required argument. Use --help to get more information on the parameters.
ERROR! Only 0 out of 1 test scripts succeeded!

run_and_check_output resolves each argument's test value from its default or
example. --output on comp_method_train.yaml merges file_pretrained_model.yaml,
which has neither, so no value is passed and the component rightly complains.

One line -- a generic example: "model" on the file spec. It has no extension, so
the harness falls back to the argument's clean name for the output path, which suits a
model artifact that is a directory for novel/simple_mlp and a single file for others.

Verified locally:

novel_train          EXIT=0  All 1 out of 1 test scripts succeeded
simple_mlp_train     EXIT=0  All 1 out of 1 test scripts succeeded

Per your note on #52 this is the generic example on the file spec; the per-method
input_model examples stay in each *_predict component's info.test_setup.with_model.