Document the "external" key provider and encryption method as non-experimental

[ghost]

Currently, the external key provider introduced in #2022 and the external method introduced in #2367 are experimental. As part of the 1.11 release, we should decide if any changes are needed and if they can be considered non-experimental. If they are moved out of the experimental phase, we should refactor the protocol implementation and possibly provide an external library.

[BeElectronicSakshi]

@cam72cam . is it open to work? Can you assign it to me?

[cam72cam]

@BeElectronicSakshi You are already assigned to https://github.com/opentofu/opentofu/issues/2379 and have not responded to that issue or posted any progress updates.

[apparentlymart]

Hi all,

We've decided to take this task out of the v1.11.0 milestone because we haven't yet heard enough feedback (whether positive or negative) about these features to know whether they are ready for stabilization.

The features are present in current OpenTofu releases and ready for use already, so this issue is only about removing the experimental notices from the documentation and treating these features as subject to our compatibility promises.

For v1.11, in https://github.com/opentofu/opentofu/pull/3323 we're going to add an additional note to the docs being explicit that these cannot be stabilized until we've got a stronger feedback signal about whether they are ready. We'll revisit this again during the v1.12 development period and hopefully stabilize it if we hear of some folks using it successfully without running into any significant design problems that we'd need to address before stabilization.

Thanks!