ENH: Allow comment lines to be written to CSV outputs. Complements read_csv's comment param

[canthonyscott]

• Tests added and passed if fixing a bug or adding a new feature
• All code checks passed.
• Added type annotations to new arguments/methods/functions.
• Added an entry in the latest doc/source/whatsnew/vX.X.X.rst file if fixing a bug or adding a new feature.

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There are many use cases (especially in the scientific community) where the best/only course of action is to enable to embedding of configuration parameters and/or other metadata into the beginning of a CSV file itself. These are typically prefaced with some comment-indication prefix such as #. This maintains human readability while attaching the metadata to the generated file itself.

Pandas' read_csv method already implements a feature to read such files and ignore these lines when parsing the the data into a dataframe. This PR implements the complement of this feature. It allows users to write these metadata and/or comment lines in their CSV outputs as well.

The to_csv method was extended to allow a comment param matching that in read_csv along with a comment_lines param which takes an iterator of strings, each of which will be written to the beginning of the file as a single line, prior to and CSV header or body data being written.

[twoertwein]

Thank you @canthonyscott for your PR. When proposing a new feature, it is typically better to first open an issue before implementing it to get feedback on the idea.

to_csv supports file handles, so a user could "easily" (but probably less convenient) have their own wrapper:

with open("test.csv", mode="wt") as handle:
    handle.write(comments)
    dataframe.to_csv(handle)

[canthonyscott]

That makes total sense. I can go open one. I may have been a little over-eager to try and see if what I wanted to do was an actual possibility first. Thank you!

[canthonyscott]

Closing this PR as discussion in the issue has led to a better solution