Hotfix/GitHub actions

[sambles]

**IMPORTANT: Please attach or create an issue before submitting a Pull Request.

Switch from Jenkins to Github actions

• Updated build and release workflows

• Updated Shiny-proxy from 1.1.0 to 2.6.1

• Updated Readme file

• [x] Shiny-proxy update breaks the current config yaml

[sambles]

replaced with https://github.com/OasisLMF/OasisUI/pull/301