kms-pkcs11 v0.2.0

This release adds support for External Keys, which are available in OpenBao starting with the upcoming v2.7 beta release.

External Key support required a rewrite of the plugin to correctly handle concurrent use of PKCS#11 sessions. A result of this rewrite is that PKCS#11 Auto Seal functionality has also seen major internal changes to work well when both Auto Seal and External Keys are used together.

This means that, while unintended, this release may include breaking changes (we can't test against all the PKCS#11 devices in the world, unfortunately!). If you run into problems that were not present in v0.1.0 (or in OpenBao v2.6.x, if you're upgrading from there), please:

1. Open an issue in https://github.com/openbao/go-kms-wrapping

2. Stay on v0.1.0 for the time being. v0.1.0 works exactly as was built into openbao-hsm v2.6.x.

Thank you!

For testing purposes, note that v0.2.0 is also compatible with OpenBao v2.6.x, so updated Auto Seal functionality can be tested ahead of v2.7. Also note that a downgrade from v0.2.0 to v0.1.0 is not possible if OpenBao re-wraps the root key, though there should be no reason to downgrade if the plugin is able to serve that operation successfully.