[TESTING] Store the current version of the most recent release in a file, for e2e tests

[aepfli]

All our tests maintain the version for their docker images to be used independently via test containers. However, this repo is integrated as a submodule to fetch gherkin files.

We can use this submodule to provide a version file, which all of our SDKs can load to start the currently appropriate testbed docker image.

• java: https://github.com/open-feature/java-sdk-contrib/blob/main/providers/flagd/src/test/resources/flagdTestbed.properties
• js: https://github.com/open-feature/js-sdk-contrib/blob/main/libs/shared/flagd-core/src/e2e/index.ts#L3

Goal

• implemented a version file that is automatically updated via release-please action
• chose a format which can be easily used by many languages eg. yaml
• document the file and the purpose within the readme