Improve configuration logging: show final resolved values and overrides

[buenaflor]

Problem

When using --sentry-define arguments alongside pubspec.yaml configuration, the current logging only shows:

info: Found config from pubspec.yaml

This is misleading because it doesn't indicate that --sentry-define values are also being used and taking precedence over the pubspec values.

Expected Behavior

The plugin should clearly log:

1. Override notifications - When a --sentry-define argument overrides a value from pubspec.yaml or sentry.properties:

   info: 'release' overridden by --sentry-define: "1.0.0" (was: "0.9.0" from pubspec.yaml)
   

2. Final resolved configuration - At debug level, show what values are actually being used:

   debug: Resolved configuration:
     - release: 1.0.0 (from --sentry-define)
     - project: my-project (from pubspec.yaml)
     - org: my-org (from environment variable)
     ...
   

Current Behavior

The merge logic in ConfigurationValues.merged() silently picks the highest-precedence value without any logging:

version: args.version ?? file.version,

Benefits

• Easier debugging when configuration isn't working as expected
• Clear visibility into which configuration sources are being used
• Helps users understand the precedence order (env vars > args > file)

Implementation Notes

• Override warnings could be logged at info level
• Full resolved config could be logged at debug level to avoid noise
• Should indicate the source of each value (--sentry-define, pubspec.yaml, sentry.properties, environment variable, default)

[linear]

DARTPL-37