docs: Add documentation on non-2xx status code handling

[micahjsmith]

Description

The documentation is not explicit about whether non-2xx status codes cause the request to fail and whether the user should handle 4xx codes like 429. However, from https://github.com/hashicorp/terraform-provider-http/blob/main/CHANGELOG.md#300-july-27-2022 it is clear that the request succeeds in this case and the user should in fact use a postcondition if they require a success response.

Rollback Plan

n/a - docs only change

Changes to Security Controls

n/a - docs only change

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[hashicorp-cla-app]

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[austinvalle]

Hi @micahjsmith 👋🏻, thanks for the PR!

This seems like a reasonable change to me, although you'll need to do two things before we can merge it:

1. The documentation is actually generated (make generate on your local machine) from the schema, which can be found here:

   terraform-provider-http/internal/provider/data_source_http.go

   Lines 52 to 68 in 821d4c5

   	Description: `
   	The ` + "`http`" + ` data source makes an HTTP GET request to the given URL and exports
   	information about the response.
   	The given URL may be either an ` + "`http`" + ` or ` + "`https`" + ` URL. This resource
   	will issue a warning if the result is not UTF-8 encoded.
   	~> **Important** Although ` + "`https`" + ` URLs can be used, there is currently no
   	mechanism to authenticate the remote server except for general verification of
   	the server certificate's chain of trust. Data retrieved from servers not under
   	your control should be treated as untrustworthy.
   	By default, there are no retries. Configuring the retry block will result in
   	retries if an error is returned by the client (e.g., connection errors) or if
   	a 5xx-range (except 501) status code is received. For further details see
   	[go-retryablehttp](https://pkg.go.dev/github.com/hashicorp/go-retryablehttp).
   	`,

   So you'll need to update that location as well (eventually when we run the CI you'd get an error message describing that).
2. HashiCorp requires that you sign the CLA agreement before we can merge the PR, it looks like our internal bot added two comments to the PR, but both links should be the same: #583 (comment) . If you sign that (or already have) and the PR doesn't update to reflect that, let me know and I'll check with the folks internal who run that 👍🏻