Request: Insert or update tags

It would be nice if there was an endpoint for explicitly creating a tag. 

e.g. `POST https://dev.lunchmoney.app/v1/tag`

```json
{
  "name": string, // required
  "description": string,
  "color":  string // either one of the ones from the site, or a hex value
```

to update `PUT https://dev.lunchmoney.app/v1/tag/:tag_id`