build(docker): specify user for runner stage

[pixincreate]

Type of Change

• [x] Bugfix
• [ ] New feature
• [ ] Enhancement
• [ ] Refactoring
• [ ] Dependency updates
• [ ] Documentation
• [ ] CI/CD

Description

This PR modifies the Dockerfile to specify the user at runner stage.

Additional Changes

• [ ] This PR modifies the API contract
• [ ] This PR modifies the database schema
• [ ] This PR modifies application configuration/environment variables

Motivation and Context

From the security perspective, it is better to be a user rather than being a root. Closes https://github.com/juspay/hyperswitch/issues/7643

How did you test it?

build succeeded (tested by making a debug build):

podman build \
    --load \
    --file Dockerfile \
    --build-arg "BINARY=router" \
    --tag hyperswitch-router \
    .

Checklist

• [ ] I formatted the code cargo +nightly fmt --all
• [ ] I addressed lints thrown by cargo clippy
• [x] I reviewed the submitted code
• [ ] I added unit tests for my changes where possible

[semanticdiff-com[bot]]

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