fix: load configured protobuf marshal options

[ajavanma]

Description

Load all five protobuf.marshalOptions values when creating the client context so consuming Protobuf messages honors the documented YAML configuration. Previously the options stayed false unless supplied with --proto-marshal-option.

Add the matching environment aliases and forward resolved values, including false, to Kubernetes proxy pods. Existing explicit command-line overrides remain authoritative. Update the configuration examples and changelog.

Fixes #326. No new dependencies.

Validation:

• Reproduced the missing configuration, JSON-output and pod-environment behavior before the fix.
• make test, make lint, focused race tests, and make build docs passed.
• Tests cover all five options, default and named contexts, environment precedence, key/value JSON output, explicit false flag overrides, and pod environment forwarding.
• Docker was unavailable locally, so broker integration tests and live Kubernetes execution were not run.
• make cve-check reports the same five findings on this patch and unchanged upstream: one in the pinned gRPC dependency and four in the local Go 1.26.5 standard library. Dependencies are unchanged.

Type of change

• Bug fix (non-breaking change which fixes an issue)

Documentation

• the change is mentioned in the ## [Unreleased] section of CHANGELOG.md
• the configuration yaml was changed and the example config in README.adoc was updated
• a usage example was added to README.adoc
• tests for the changes have been implemented (see: Testing your changes)