docs: Add Telegraf features to README

[Hipska]

Closes #14475

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[tobz]

@Hipska Would you mind providing link(s) to Telegraf's documentation that detail its behavior with regards to delivery guarantees?

Our definition of "delivery guarantees" is that there is support for a source (so let's say... something writing to Telegraf using a request/response protocol) to be told that the event data it sent has been successfully processed by a sink (so wherever Telegraf happens to be sending the data).

Naturally, not all sources/inputs and sinks/outputs use a request/response protocol, so not all configurations will support delivery guarantees, but it wasn't clear from a cursory glance that Telegraf has any sort of delivery guarantee capabilities to begin with.

[Hipska]

Okay, that is indeed not something telegraf is providing. Telegraf can confirm the receiving of a metric to its input/source and is also aware of correct sending a metric to its output/sink, but there is no relation to the complete flow. I will remove that tick then..

As said in #14475, it is unclear when a tool gets a tick, so I'm open for comments.

[Hipska]

@tobz Maybe it should be outlined that the telegraf delivery guarantees are not end-to-end by the means of an icon or footnote?

[jszwedko]

Thanks @Hipska !