samples\drivers\rtc: Added rtc overlay files for stm32wba - nucleo_wba55cg and nucleo_wba65ri

[suja8742]

Fixes samples\drivers\rtc fro failing to compile for the nucleo_wba55cg and nucleo_wba65ri platforms.

Why:
To contribute other fixes for rtc interrupts, this is a good first step - Being able to run the sample.

Testing:

• Verified on nucleo_wba55cg and nucleo_wba65ri boards
• CI build passes locally

Signed-off-by: Sudarshan JAGANNATHAN

[github-actions]

Hello @suja8742, and thank you very much for your first pull request to the Zephyr project!
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[bjarki-andreasen]

The commit needs to match the zephyr contribution guidelines https://docs.zephyrproject.org/latest/contribute/guidelines.html

[sonarqubecloud]

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 SonarQube Cloud