Publish docs on push

The documentation is not being republished when new changes are pushed to the repository. This means the API can become out of step with the current codebase.

Documentation publishing used to happen with [this job](https://github.com/hyperledger/fabric-chaincode-java/blob/106cbd12c2148cc178ff9cdeb386b9462477bf56/ci/azure-pipelines.yml#L123-L161) in the Azure Pipelines build. The use of the GitHub Actions deploy-pages action (as used in the [fabric-gateway build](https://github.com/hyperledger/fabric-gateway/blob/e393353237f51a0ddd23e2ae3f7a7e4a8e9b5a6c/.github/workflows/push.yml#L15-L53)) might be a good approach to use.