Expose flux generate feature in the UI to auto-generate test data

Thank you for suggesting an idea to improve InfluxData UI.

**Proposal:**
The flux generate function can generate test data. By creating a task like this one, we can auto-fill a bucket with test data:

import "generate"
import "experimental"
option task = {name: "Generate the number 5", every: 10s}
generate.from(
count: 1,
fn: (n) =>
(5),
start: -task.every,
stop: task.every,
)
|> map(fn: (r) =>
({r with _measurement: "five", _field: "likeTheNumberFive"}))
|> to(bucket: "devbucket")

**Current behavior:**
Today you can upload line protocol or a CSV file to generate test data, but that is a single point in time. This capability would generate ongoing time series data.

**Desired behavior:**
Make it easy for end users to generate test data. This could either potentially go in the notebooks UI somewhere, or in the load-data area of the UI, whichever is more intuitive.