[5.1] docs(charts): update trendline articles to include the new types

[xristianstefanov]

Related to: https://github.com/telerik/blazor/issues/7966.

[ikoevska]

General notes from the review:

• You don't really need the monospace formatting in the bulleted list at the beginning of the page. In fact, you can drop it from all instances. It makes sense to use monospace formatting if you're using the correct spelling used in the code.
• I took the liberty of suggesting a "Use X to achieve Y" template for the descriptions of the charts. It's more action-oriented and provides clear goals at a glance. Feel free to rework the suggestions as needed, if I messed up the accuracy.
• Personally, I wonder if Supported Series should be moved to the beginning of the page. So that if you're working with something that's not supported, you could safely skip the page.
• This one seems out of the scope of these changes, but I would have loved to see a more detailed explanation about how to configure/implement trendlines (I know it's obvious in the code, but ideally, there would be a section/a paragraph/one line saying where and when in your code it's appropriate to implement it, possibly, a general template or any extra info needed to make it work, what are some best practices for Blazor trendlines (if any), tips and tricks (or links to them, possibly links to applicable KBs), styling.

[ikoevska]

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