[Feature Request] Possibility to export tags

[Cygon]

Describe the feature
I'd like to preserve the tags present on e621 in my local copy.

As it stands now, all I can do with the local copy is look at the images of one artist (or pool), but the feature of looking for finign specific content by tag is lost.

Having tags as a .csv file (i.e. one line per image id containing said image id and all its tags comma-separated) would be useful to try and import the tags into self-hosted/standalone image managers like Hydrus, Photonix, EagleApp or iTag.

Perhaps this would also be interesting for the stable diffusion AI crowd (w/coprighted blacklisted and/or keeping the resulting model and images to oneself?).

To Reproduce
Steps to reproduce the behavior:

1. Run e621_downloader as intended
2. Notice that only the image ids are downloaded and the tags are lost

Expected behavior
At 2. to find some .csv file or other, containing the associated tags for each image id

Desktop (please complete the following information):

• OS: Gentoo Linux, stable tree, KDE5 Plasma
• e621_downloader Version: 1.7.2

Additional context
Add any other context about the problem here.