feat(processors/parser): Add option to parse tags

[Hipska]

Required for all PRs:

• Updated associated README.md.
• Wrote appropriate unit tests.
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Add an option to also parse tags (as the example config description was already saying that).

I don't have added tests yet. If someone could tell me the test(name)s I should add, I'm happy to implement them..

[telegraf-tiger]

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[reimda]

Couldn't you use the converter processor to switch a tag to field, then use the parser plugin on the field?

[Hipska]

True, but the sample config already mentioned tags. Other processors also work on both tags and fields.

[Hipska]

Also, the number and names of resulting fields after the parse could be dynamic, so difficult to catch them all.

Nevermind, after this PR the resulting new tags/fields will still be based from the chosen parser and its configuration. I made another PR to handle that: #11060

[Hipska]

So @reimda, WDYT?

[Hipska]

@reimda ?

[Hipska]

Followed-up by #11228