Clean up transform steps (and native plugins generally)

[dominiklohmann]

This follows up on an internal discussion to rename some transform step before the upcoming major release of VAST v2.0 to align their names with what we generally deemed most suitable.

Here's a summary of the changes:

• The rename step can now rename fields as well as schemas.
• The where step supersedes both the filter and select steps.
• The delete step is now called drop.
• The project step is now called put.
• The replace step now supports all complex types that can be inferred.
• The aggregate step is now called summarize.

And lastly, developer-facing only:

• Native plugins no longer need to be explicitly registered in the CMakeLists.txt file of libvast.
• It is now harder to misuse native plugins code by calling it directly from libvast; instead, calls must now go through the plugin API. This supersedes Simplify native plugins setup #2220.

📝 Checklist

• All user-facing changes have changelog entries.
• The changes are reflected on docs.tenzir.com/vast, if necessary.
• The PR description contains instructions for the reviewer, if necessary.

🎯 Review Instructions

Review the description. Then read the code commit-by-commit.

Before merging this still needs a documentation update.

[mavam]

Looks good! CI will sanity-check this.

I have some small cosmetic comments only.