docker: Bump oasis-cli to 0.15.3

[ptrus]

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[Copilot]

Pull Request Overview

This PR updates the oasis-cli version from 0.15.2 to 0.15.3 and fixes an issue with JSON parsing in the command output handling. The change separates stdout from the combined output buffer to ensure proper parsing of JSON responses from push commands.

• Bump oasis-cli version to 0.15.3 in Docker configuration
• Fix JSON parsing by using separate stdout buffer instead of combined logs
• Add changelog entry for the version update

Reviewed Changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated 1 comment.

File	Description
docker/Dockerfile	Updates OASIS_CLI_VERSION from 0.15.2 to 0.15.3
worker/oasiscli/oasiscli.go	Separates stdout from combined output and fixes JSON parsing to use stdout buffer
.changelog/82.feature.md	Adds changelog entry for the oasis-cli version bump

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