Create terraform.io Documentation for Terraform Logging Functionality

[bflad]

Does this documenation exist?

• This is new documentation
• This is an enhancement to existing documentation

Where would you expect to find this documentation?

(either or both)

• On terraform.io
• In the GoDoc for this module
• In this repo as a markdown file
• Somewhere else

Details

Proper log handling in Terraform is complex! Between trying to understand that Terraform CLI uses the process stderr and not the gRPC stderr stream and the plethora of TF_LOG* environment variables that are available to control logging.

Description

Ideally, this documentation would start with the most common use cases with the interactions/configurations involved, then dive into deeper concepts:

• Practitioners configuring logging for normal Terraform runs (this can/should be a link to terraform.io documentation)
• Provider developers configuring logging for a test framework runs
• SDK developers implementing logging in a SDK or test framework

@paddycarver drew up an excellent little whiteboard sketch that helps show the interaction between a test framework implementing this package and the various spun up processes and environment variables. It would be great to include diagrams like these as editable images in this repository.

References

• Build in log sink functionality. #9 (comment)
• Come up with a testing strategy for the logging sink #11

[bflad]

Initial documentation has been shipped:

• https://www.terraform.io/plugin/log/managing
• https://www.terraform.io/plugin/log/writing

We'll separately create "Logging" pages under SDKv2/Framework to capture special environment variables, logging keys, implementation details, etc for each framework.

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