Online API documentation

[quinmars]

The UaClient library is missing an online API documentation. The goal should be that there is an up-to-date (in sync with the master branch) online documenation. With github pages and workflows, this shouldn't be too difficult to automate the generation and deployment. A github page already exists for opc-ua-client. One can choose from several documentation generation tools: sandcastle, docfx and wyam, to name some. I favor docfx, since it seems to be easy to setup and has a pleasant output. There already exists some github actions to automate the generation and deployment process, namely nikeee/docfx-action and maxheld83/ghpages
.

If you like, I'll try to setup the doxfx configuration and the CI integration.