Fix egress proxy ARM64 build by using Alpine edge repository

[JAORMX]

Problem

The egress proxy Docker image build is failing for ARM64 architecture because the `squid` package is not available in Alpine Linux 3.22.1 repositories for the `aarch64` architecture.

Changes

This PR adds the Alpine edge community repository to the Dockerfile to access the squid package for both AMD64 and ARM64 architectures.

Modified Files:

• `containers/egress-proxy/Dockerfile`: Added Alpine edge repository before installing squid

Testing

• ✅ Local build test for `linux/amd64` - PASSED
• ✅ Local build test for `linux/arm64` - PASSED

Both architectures now successfully build the egress proxy image.

Impact

• Fixes: Multi-architecture Docker image builds for egress proxy
• Severity: High - Previously blocked all ARM64 builds
• Risk: Low - Uses official Alpine edge repository

Fixes #1994

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 47.42%. Comparing base (7138ac9) to head (2d3f9e6).
⚠️ Report is 1 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1995      +/-   ##
==========================================
+ Coverage   47.36%   47.42%   +0.05%     
==========================================
  Files         232      232              
  Lines       28644    28644              
==========================================
+ Hits        13568    13583      +15     
+ Misses      14059    14039      -20     
- Partials     1017     1022       +5     

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[Copilot]

Pull Request Overview

This PR fixes the egress proxy Docker image build failure for ARM64 architecture by adding the Alpine edge community repository to access the squid package, which is not available in Alpine Linux 3.22.1 repositories for aarch64.

• Adds Alpine edge community repository before installing squid
• Enables multi-architecture builds for both AMD64 and ARM64
• Updates comment to reflect the use of edge repository

---

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[Copilot]

Adding the Alpine edge repository introduces potential security and stability risks since edge packages are not stable releases. Consider adding apk update after adding the repository to ensure the latest package index is used, and document that this is a temporary workaround until squid becomes available in the stable ARM64 repositories.

Suggested change

	# Install squid from edge repository and create necessary directories
	RUN echo "https://dl-cdn.alpinelinux.org/alpine/edge/community" >> /etc/apk/repositories \
	# Temporary workaround: Install squid from edge repository because it is not yet available in the stable ARM64 repositories.
	RUN echo "https://dl-cdn.alpinelinux.org/alpine/edge/community" >> /etc/apk/repositories \
	&& apk update \