and "[advanced][algorithms][pca] Fixed v1 declaration"

This reverts commit c4bd73dd.
and commit ffbd06c1.

While the default value can be strings rather than numerical,
they are still handled properly.

However, since the online platform already contains experiments
ran with these "wrong" declaration and to ensure it's coherence,
the examples for API V1 will be kept as is and the schema
validation for v1 will take into account that.

This will allow to keep the current system untouched and ensure
future algorithms to be written correctly.