Joplin UI for adding simple tables

### As a content editor, I want to be able to add a simple table to display information like fee structures, so that I can better communicate this kind of information to residents

### As a content editor, I need to be able to add basic tables to a service or info page, so that I can sensibly display fees charts or similar content.

- [ ] design team delivers designs for how a content editor adds a table within a Joplin rich text block

Per #1936, @chasechenevert has been designing how tables display on Janis. We'll also need to design how a content editor can add a table via the author interface.

Scope question: should we limit this to fee tables for now, or design for other use cases as well? (And does it matter?)

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**Current experience:** authors have to use markdown using the `` button within a rich text block.
When adding a markdown table to Joplin, use [this tool](https://stackedit.io/app#) to generate table markdown.
When entering into Joplin, use Shift+Return (on the keyboard) so the markdown stays as all one block.