Training UI: Update Training Images section

- [x] In "Training images" section, update text from "Image directory" to "Curated image data CSV"
- [x] Update the guide text from "Accepts CSV files, see instruction" to "See instructions for CSV file", link TBD

### Size
XS

### Scope
We won't be worry about validating csv file within the plugin (cyto-dl does that) and the error reported from cyto-dl backend on wrongly formatted CSV (yet). We're counting on the guide text to show user how to correctly format their CSV file .

### Additional Notes
V1 deliverable
- [ ] Remove [Browse] button - check on May 7 meeting