Improve build workflow and release process (#200)

* Merge docker workflow into the build one. Create release on successful build.

* Asset upload implementation and fixes

* Add release template and body update on release build

* Build binaries table automatically with minor verification improvements

* Adding docker image section and polishing release process documentation

* Refactor build to remove duplicated code

* Fix ShellCheck warnings and recommendations

* Fix for passing variable value in logs

* Improved release update

* Use published links for binaries table

.github/release_template.md

@@ -0,0 +1,43 @@
+[comment]: <> (This is a comment, it will not be included in the final release notes.)
+[comment]: <> (This template will be used to automatically generate release notes with the ci-build workflow.)
+[comment]: <> (The following values will be automatically replaced with generated content from the workflow.)
+[comment]: <> (`[GENERATED-RELEASE-NOTES]`: Replaced with the GitHub generated release notes.)
+[comment]: <> (`[WORKFLOW-URL]`: Replaced with the link to the workflow that generated the build.)
+[comment]: <> (`[BINARIES-TABLE]`: Replaced with the a markdown formatted table with a link to each binary download.)
+[comment]: <> (`[DOCKER-TABLE]`: Replaced with the a markdown formatted table with a link to the docker image.)
+
+# Summary
+
+`[Add a small summary here]`
+
+# Known Issues
+
+`[Remove this section if there is no known issue]`
+
+# All changes
+
+`[GENERATED-RELEASE-NOTES]`
+
+# Building process
+
+Release assets were built using Github Actions and [this workflow run](`[WORKFLOW-RUN-URL]`). You can establish the provenance of this build using [our artifact attestations](https://github.com/eth-educators/ethstaker-deposit-cli/attestations).
+
+With [the GitHub CLI](https://cli.github.com/) installed, a simple way to verify these assets is to run this command while replacing `[filename]` with the path to the downloaded asset:
+
+```console
+gh attestation verify [filename] --repo eth-educators/ethstaker-deposit-cli
+```
+
+This step requires you to be online. If you want to perform this offline, follow [these instructions from GitHub](https://docs.github.com/en/actions/security-for-github-actions/using-artifact-attestations/verifying-attestations-offline).
+
+# Binaries
+
+`[BINARIES-TABLE]`
+
+# Docker image
+
+`[DOCKER-TABLE]`
+
+## License
+
+By downloading and using this software, you agree to the [license](LICENSE).