feat: add refer option to export conversation.json using API

[moonmd]

Rebased #268
Refers conversations.json to the API for export

[pionxzh]

With the information from #272, I now understand the issue. To handle this problem, I want to do a bigger rework on the export dialog. But it means I cannot merge this PR. I'm sorry about that. 🙏 I feel "refer" would be difficult for users to understand what it is for.

[pionxzh]

something like this

[moonmd]

Good idea to break it out to chunks because selecting that many conversations is tedious.
I was trying to figure out a way to shift-select groups, but I couldn't get the shift key to be detected.
"Load All" will never finish if you don't make it "Load 1000". Maybe continue with that concept and give some options.
Load: 100 250 500 750 1000

Also, with a 1000 conversations, it takes a long time to build the zip files. You may want to add a status bar showing that it is still working on it.