Allow prefix in spring-cloud-starter-aws-secrets-manager-config without forward slash

[vamsi245]

Is your feature request related to a problem? Please describe.
spring-cloud-starter-aws-secrets-manager-config takes a prefix with a forward slash

Describe the solution you'd like
Change the class to accept prefix without forward slash. Some companies have policies to restrict secretsmanager creation with forward slash

Describe alternatives you've considered
None

Additional context
https://cloud.spring.io/spring-cloud-aws/2.1.x/multi/multi__cloud_environment.html

[eddumelendez]

we are discussing about naming properties keys in this issue. I will close this in favor of that one.