Add additional formats to annotation export

[dwhly]

Adding additional format types for export will dramatically increase the utlity of this feature. Proposed: Add CSV, TXT and HTML formats in addition to JSON. This will require UX to specify these additional format types, such as:

Also, the exact structure that each file format has will need to be defined. Here is a google doc with some provisional descriptions for each.

https://docs.google.com/document/d/1Xn6AazKkpUy85VUaj9v_utasexk8lIqP_1zveILq1So/edit

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• [x] Create FF
• [x] Add format selection dropdown
• [x] Implement logic to export plain text file
• [x] Implement logic to export CSV file
• [x] Implement logic to export HTML file
• [x] Implement copy-to-clipboard

[robertknight]

Less technical users probably won't know what the use of the different formats are. It could be helpful to spell that out in the dropdown. Something along the lines of:

JSON - For import into another Hypothesis group or document CSV - For import into Excel, Google Sheets etc. TXT - Plain text HTML - Rich text

[jaredpdesigns]

Here's some revised elements shuffled around including the "Copy to Clipboard" option:

[acelaya]

I have created a project board for a more detailed progress tracking https://github.com/orgs/hypothesis/projects/131/views/1

[acelaya]

I'm going to close this as completed, as the bulk of the work is done, and the main user journey is finished.

The feature is currently disabled behind a feature flag, but we will soon enable it for public users.

There's a few pending improvements that can be tracked separately. Main ones are tagged as project: export formats, and a few more can be found in the project board.