DRAFT: add opensign app

[mtahle]

Hi,
this is my first contribution, and I would like to contribute more in the future. Unfortunately the deployment still no working will so I opened this PR hope to get some help from you

☑️ Self Check before Merge

• [x ] I have tested the template using the method described in README.md thoroughly but it didn't work with me
• [x ] I have ensured that I put as much default values as possible (except passwords) to ensure minimum effort required for end users to get started.
• I have ensured that I am not using the "latest" tag as this tag is dynamically changing and might break the one-click app. Use a fixed version.
• [x ] I have made sure that instructions.start and instructions.end are clear and self-explanatory.
• Icon is added as a png file to the logos directory.
• I've executed the checks if necessary by running npm ci && npm run validate_apps && npm run formatter (If failling run the prettier: npm run formatter-write)
• [x ] I will take responsibility addressing any issues that arises as a result of this PR (maintaining this app).