Differentiate Task request schemas where different properties are required

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For cloud, a Task must have one of `flux` or `scriptID`. If it has `scriptID`, then it may have other fields (that aren't compatible with `flux` in a create request).
Differentiating the schemas with `oneOf` breaks the current UI tests--e.g.:

> @jstirnaman
>
> ```
> src/tasks/containers/TaskPage.test.tsx:259:66 - error TS2339: Property 'flux' does not exist on type 'TaskCreateRequest | TaskWithScriptCreateRequest'.
> Property 'flux' does not exist on type 'TaskWithScriptCreateRequest'.
> ```

I'm assuming it needs a discriminator to know which schema to use? I ran `yarn generate` to generate `src/client/*` locally and I don't even see `TaskWithScriptCreateRequest` in the results, so I 'm confused.
I'll undo this for now and move it to my _someday_ list. It seems beneficial to clients if they could discern which properties are compatible and required. I hate having it in human-readable-only fields.

_Originally posted by @jstirnaman in https://github.com/influxdata/openapi/pull/591#discussion_r1010901842_

Start with the schema changes discussed in pull request 591 and the generated output under src/client. Run yarn generate, then inspect src/tasks/containers/TaskPage.test.tsx around line 259 to understand the current type error. Done means the generated client exposes the differentiated Task request properties while the existing UI tests type-check.

Written by the indexing model from the issue text.