feat: support modal background opacity through CustomJson (RMCCX-7327)

[maureenorea-clores]

Description

• Support background opacity setting for modal capaign
• Improve CustomJson deserializer

Links

RMCCX-7327

Checklist

• I have read the contributing guidelines.
• I wrote/updated tests for new/changed code
• I removed all sensitive data before every commit, including API endpoints and keys, and internal links
• I checked that all possible internal and platform/library exceptions are gracefully handled and will not crash the host app
• I checked for open & known issues (especially crashes) for any newly added platform APIs or libraries
• I tested non-trivial changes on a real device
• I added ticket/changes in changelog
• I ran ./gradlew check without errors

[sonarcloud]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarCloud

[rakutentech-danger-bot]

	2 Warnings
⚠️	Branch name "feat/RMCCX-7327_dark-background" should match format: <type>/<ticket-no>_<short-desc> or <type>/<short-desc> or release/<version or desc>.
⚠️	PR title "feat: support modal background opacity through CustomJson (RMCCX-7327)" should append ticket number(s).

JaCoCo Code Coverage 97.35% ✅

Class	Covered	Meta	Status
com/rakuten/tech/mobile/inappmessaging/runtime/view/InAppMessageModalView	100%	0%	✅
com/rakuten/tech/mobile/inappmessaging/runtime/data/responses/ping/Message	93%	0%	✅
com/rakuten/tech/mobile/inappmessaging/runtime/data/customjson/CustomJsonDeserializer	50%	0%	✅
com/rakuten/tech/mobile/inappmessaging/runtime/data/customjson/CustomJson	100%	0%	✅
com/rakuten/tech/mobile/inappmessaging/runtime/data/customjson/MessageMapper	100%	0%	✅
com/rakuten/tech/mobile/inappmessaging/runtime/data/ui/UiMessage	94%	0%	✅

Generated by 🚫 Danger

[mdusmangani-jp]

LGTM