Add `data.http` data source

[traut]

Background

In cases when a fitting data source is not available and it's not possible to use local data files, it would be helpful to have a data source that can fetch data from an URL.

Design

Following an example of Terraform's http provider, implement data.http data source.

Eval parameters:

• url
• method
• basic_auth_username
• basic_auth_password
• insecure
• timeout_secs
• headers
• body

References

• https://github.com/hashicorp/terraform-provider-http
• https://registry.terraform.io/providers/hashicorp/http/latest/docs/data-sources/http