SWI-11363 docs: add GitHub issue templates for bug and feature reports

[kshahbw]

What

Adds structured GitHub issue templates under .github/ISSUE_TEMPLATE/, mirroring the guidance already in CONTRIBUTING.md.

• bug_report.yml — follows the "How to report a problem" checklist: what you were doing, expected vs. actual (with the fail-loudly note), a minimal XML repro, environment, and a required confirmation that credentials/PII are scrubbed.
• feature_request.yml — problem → proposal → workarounds, with a nudge that translation support is driven by src/matrix/twilio-voice.json and a reminder that this is best-effort.
• config.yml — keeps blank issues enabled, and adds contact links routing SLA-backed support to the Bandwidth account team and pointing to CONTRIBUTING.md.

Notes

Config-only change — no code, tests, or behavior affected. YAML validated locally.

[bwappsec]

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