feat: Add LinkContentFetcher Haystack 2.0 component

[vblagoje]

Why:

This PR introduces the LinkContentFetcher component to Haystack 2.0. This component is responsible for fetching content from a given URL and converting it into a Document object, which can then be used within the Haystack 2.0 pipeline.

Part of #5614

What:

A new LinkContentFetcher component has been added to the newly created fetchers package. This package is intended to be the future home for all components that fetch data via network calls.

How can it be used:

Here's a code snippet demonstrating how to use the new LinkContentFetcher component:

from haystack.preview import Document
from haystack.preview.components.fetchers import LinkContentFetcher

lcf = LinkContentFetcher()
doc: Document = lcf.fetch(url="example.com")
print(doc)

How did you test it:

Unit tests have been added to cover the new component. Additionally, manual tests were conducted, as described in the "How can it be used" section above.

Notes For Reviewer:

Please ensure that the new component and its unit tests are correctly implemented.

[ZanSara]

Implementation is solid but I think it can be simplified a lot. Sorry that I left many comments, I tried to provide the code where possible.

[ZanSara]

I've just realized that there's no proper way to store the binary returned with the response into the current Document class. As this is not the first time we have trouble with the limitations of Document, I'm going to first expand the Document class and then wrap up this PR.

[coveralls]

Pull Request Test Coverage Report for Build 6245834225

• 0 of 0 changed or added relevant lines in 0 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage increased (+0.1%) to 49.255%

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Totals
Change from base Build 6244882304:	0.1%
Covered Lines:	11904
Relevant Lines:	24168

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💛 - Coveralls

[ZanSara]

🚀