fix: Rename preview package file_converters to converters

[vblagoje]

Why:
The purpose of this pull request is to rename package file_converters to converters. This change is aimed at broadening the scope or improving the clarity of the component names.

What:
The modifications included renaming various elements of the codebase, from directories and files to references within the code. Renaming affected components like TextFileToDocument, TikaDocumentConverter, and others. Additionally, the related documentation and tests have been updated to correspond with these new names.

How can it be used:
Post-renaming, developers using the haystack library should now look for components under the converters namespace rather than file_converters. For example, the use of HTMLToDocument will transition from haystack.preview.components.file_converters.html import HTMLToDocument to haystack.preview.components.converters.html import HTMLToDocument. This change impacts how users will import and utilize these components in their pipelines or code.

How did you test it:
Testing details have not been explicitly provided in the provided data. Typically, the testing procedure would involve running the existing unit tests ensuring all pass with the new naming convention. Additionally, ensuring that any documentation and quick-start guides reflect the changes to assist users in transition would be part of the testing procedure.

Notes for the reviewer:
Reviewers should focus on validating the completeness of the renaming process across the codebase. This includes ensuring that all instances of the old file_converters namespace are appropriately updated, verify that no references have been missed, and ensuring backwards compatibility or providing clear migration paths for users. Reviewers might also check for consistent naming conventions, proper documentation updates, and rerun all unit tests to confirm they pass with the updated names. It is also important to verify that any public APIs or exposed functionalities remain consistent or are properly documented if there are changes.

[vblagoje]

@dfokina would you please have a look that I changed only docs-related stuff in the preview and not the old one 🙏

[silvanocerza]

Looks good 👍