Add TLS configuration to backend http client

[fridgepoet]

What this PR does / why we need it:

Which issue(s) this PR fixes:

Fixes #111

Special notes for your reviewer:

[github-actions]

Levitate is-compatible report:

🔍 Resolving @grafana/data@latest...
🔍 Resolving @grafana/ui@latest...
🔍 Resolving @grafana/runtime@latest...
🔍 Resolving @grafana/e2e-selectors@latest...

🔬 Checking compatibility between ./src/module.ts and @grafana/data@9.4.7...
✔ Found @grafana/data version 9.0.2 locally

🔬 Checking compatibility between ./src/module.ts and @grafana/ui@9.4.7...
✔ Found @grafana/ui version 9.0.2 locally

🔬 Checking compatibility between ./src/module.ts and @grafana/runtime@9.4.7...
✔ Found @grafana/runtime version 9.0.2 locally

🔬 Checking compatibility between ./src/module.ts and @grafana/e2e-selectors@9.4.7...
✔ Found @grafana/e2e-selectors version 9.0.2 locally

✔️ ./src/module.ts appears to be compatible with @grafana/data,@grafana/ui,@grafana/runtime,@grafana/e2e-selectors

[github-actions]

Backend code coverage report for PR #113

Plugin	Main	PR	Difference
opensearch	43.4%	43.4%	0%

[github-actions]

Frontend code coverage report for PR #113
No changes