Load secret as string if json parse fails

[snigdhasjg]

📢 Type of change

• Bugfix
• New feature
• Enhancement
• Refactoring

📜 Description

If secret is not a JSON string, it will take it as string.
Name of spring property will be secret name last suffix.
eg. if secret name is service1/secret1 the property name will be secret1.
Similar approach as 3.0.x

This also inherits behaviour like adding prefix to the property name.

💡 Motivation and Context

Fixes #636

💚 How did you test it?

Unit test only.

📝 Checklist

• I reviewed submitted code
• I added tests to verify changes
• I updated reference documentation to reflect the change
• All tests passing
• No breaking changes

🔮 Next steps

[maciejwalkowiak]

Thanks @snigdhasjg !