Expose toggle for `allowInsecure` when creating new scrapers

**Proposal:**
Add a checkbox to the "Create Scraper" dialog to enable setting the "allowInsecure" parameter, which is useful for scraping systems behind self-signed TLS certificates.

**Current behavior:**
The dialog looks like this:
As far as I know, the UI doesn't set the `allowInsecure` field when you submit the form, so it falls back to its default value of `false` as spec'd [here](https://github.com/influxdata/openapi/blob/master/contracts/oss.yml#L12120-L12123).

**Desired behavior:**
Add an extra checkbox / toggle to the form to allow setting `allowInsecure`, and have the value of the box pass through to the API request.

**Alternatives considered:**
Users can bypass the UI to create scrapers via direct API calls (see [this](https://community.influxdata.com/t/how-to-configure-scraper-to-skip-validation-on-self-signed-certificates/20381/2?u=dan-moran) for example).

**Use case:**
The OSS 2.0.2 [release notes](https://docs.influxdata.com/influxdb/v2.0/reference/release-notes/influxdb/#v202-general-availability-2020-11-19) mention that `allowInsecure` is now supported for scrapers, but users don't see any way to use it. The `influx` CLI doesn't currently support scraper management, so the UI is currently the easiest place to add a toggle.