Add Solace PubSub+ instructions for Copilot

[sumitkc]

Summary

• Adds .github/instructions/solace.instructions.md so Copilot applies the team's Solace messaging conventions when editing Java code.
• Covers library choice (solace-spring-boot-starter), config (no hardcoded broker URLs), topic naming (<domain>/<bounded-context>/<version>/<event>), QoS (Persistent vs Direct), producer/consumer shape, DMQ handling, reconnection, logging/observability, and testing (Testcontainers for integration).
• Mirrors the format of the existing spring-boot.instructions.md (numbered sections, applyTo frontmatter, terse rule-style prose).

Test plan

• Confirm applyTo: "**/src/main/**/*.java" is the desired scope (could be narrowed to **/*Publisher*.java/**/*Subscriber*.java if preferred).
• Review wording/opinion of each section against the team's actual Solace setup — adjust topic-naming examples or QoS defaults if they diverge.
• Verify the file renders correctly in Copilot's instructions picker.

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