test: Improving conftest.py so that local configuration is handled

[a-bouth]

Adapted conftest.py in such way that it is transparent for the user to use whether he's in local or "docker" configuration with the DPF Server.

Main Changes

• We use a gRPC configuration for the local server and make it global, in connect_to_or_start_server
• All tests files are now uploaded on the server side and the paths are uploaded accordingly, the path will always be the correct one either in local or docker configuration
• Exception made for flute_psd.txt this file is needed only locally as we're using native python functions to read it and not DPF Operators
• The fixture dpf_sound_test_server is not needed anymore, everything is done in pytest_configure
• The functions get_absolute_path_for* are not relevant anymore and caused maintainability problems so I removed them (and thus removed the file _get_example_file.py, don't panick, there's still download.py that collect files for our examples and is still very relevant)

Side Changes

• In source_control_spectrum I had a text formatting error locally, I changed the syntax but the result is the same
• In tests for prominence_ratio and tone_to_noise_ratio there was a missing fixture show_mockup for plot tests that caused a bug, I added them
• In tests for prominence_ratio and tone_to_noise_ratio I changed the way we obtained `flute_psd.txt

Doc

https://dpf.docs.pyansys.com/version/stable/getting_started/dpf_server.html

[ansaminard]

Just a minor suggestion with no functional impact.
Also a question, will that allow us to add tests for existence of input files in feature classes? ( I remember we ran into an issue before when doing such tests because of the ambiguity of the file location between the host machine and the server)

[a-bouth]

Just a minor suggestion with no functional impact. Also a question, will that allow us to add tests for existence of input files in feature classes? ( I remember we ran into an issue before when doing such tests because of the ambiguity of the file location between the host machine and the server)

@ansaminard probably no, because the feature classes should not be aware of whether they're in "Docker" or "local" configuration

With the changes I've done in my PR, we know where the files are as long as we have access to the server variable

I'm trying to think of a way of doing that while writing those lines but all solutions that come to mind seems way too complex

For the tests and the documentation, we're in a controlled environment, with as many input file paths as we have users, this will probably be too complex