Manual tagging system

Hey, I just wanted to start of saying that this is a crazy awesome project and thanks to everyone working on it <3

_(TL;DR at the bottom of the issue)_

I think it could be cool to have some sort of a manual tagging system. This might be a bit too big of a feature request at this point, but I couldn't find anyone talking about this, nor information on whether this exists already or not. I did see you could search with tags already, but that seems to be referencing tags that are in the metadata of the files themselves, right? I am proposing a system in which the user themselves can manually assign any number of tags to a file to use for search later.

**Is your feature request related to a problem? Please describe.**

Lets say, hypothetically, me and my friends were storing a lot of memes from over the years. Now, long while later, I'd like to go back and find something particular. I knew the meme had a cat and some music and I was actively tagging files with my own custom tags. So if this was the case, I could search for files that I have tagged with "cat" and "music".

**Describe the idea / solution you'd like**

A system of adding/removing/editing/searching by user-created tags. You could upload a file and optionally add tags to them yourself, by which you could try to look them up later. Could be nice to have some searching logic, so you could include as well as exclude tags in you search. If it's too much in the way, it could maybe also be a feature you can enable/disable?

Another step would be to have a way of connect tags that are synonyms, so I could say I want tags "cat" and "feline" to be considered the same tag. This way, something tagged with "feline" could be found by searching for the "cat" tag. At this point, the tagging system would probably need a dedicated page just for managing tags.

**Who else might benefit?**

Now I don't know for sure, but I imagine there are others who might find a use for something like this, maybe? Maybe a video editor wants to find a specific kind of b-roll footage out of hundreds of clips. If the clips had been tagged during upload, this could make it a lot easier!

**Describe any alternatives you've considered**

One way you could manage is to simply make the filenames obvious enough for searching, but I'd find a tagging system much more preferable. Ive also dabbled in this with my own projects, but never finished any good system. I am considering writing a completely separate little web app that just keeps track of tags and allows me to manage and search tags assigned to files uploaded via copyparty. Another option is to just not use copyparty and use something else that has been created specifically for this purpose. But I like copyparty-

**TLDR User-managed tagging system like on image boards.**