Wave v1.15.1

Feature updates and improvements

• Check block existence with object operation by @pditommaso in https://github.com/seqeralabs/wave/pull/750
• Add /v1alpha2/validate-creds endpoint by @pditommaso in https://github.com/seqeralabs/wave/pull/752
• Switch env vars around by @justinegeffen in https://github.com/seqeralabs/wave/pull/748

Full changelog: https://github.com/seqeralabs/wave/compare/v1.15.0...v1.15.1