Add multiple node postprocessors

[Dedalo314]

Multiple node postprocessors can now be used instead of just one.

What does this PR do?

Allows multiple node postprocessors, such as similarity and metadata postprocessors. They are executed in the same order of the list.

Before submitting

• Did you make sure title is self-explanatory and the description concisely explains the PR?
• Did you make sure your PR does only one thing, instead of bundling different changes together?
• Did you list all the breaking changes introduced by this pull request?
• Did you test your PR locally with pytest command?
• Did you run pre-commit hooks with pre-commit run -a command?

Did you have fun?

Make sure you had fun coding 🙃