chore: use class methods to create ChatMessage

[anakin87]

Related Issues

• part of Migration of experimental ChatMessage to Haystack #8583
• with the migration of the experimental ChatMessage into Haystack, creating instances using the dataclass constructor will likely break; class methods will not break instead

Proposed Changes:

• wherever possible, replace usage of dataclass constructor with the appropriate class method

How did you test it?

CI

Checklist

• I have read the contributors guidelines and the code of conduct
• I have updated the related issue with new insights and changes
• I added unit tests and updated the docstrings
• I've used one of the conventional commit types for my PR title: fix:, feat:, build:, chore:, ci:, docs:, style:, refactor:, perf:, test:.
• I documented my code
• I ran pre-commit hooks and fixed any issue

[coveralls]

Pull Request Test Coverage Report for Build 12028566042

Details

• 0 of 0 changed or added relevant lines in 0 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage remained the same at 90.3%

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Totals
Change from base Build 12027959745:	0.0%
Covered Lines:	7987
Relevant Lines:	8845

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💛 - Coveralls