Spring Boot 2: StageName should be stripped from the path by default

*Serverless Java Container version*: 1.5.2

*Implementations:* Spring Boot 2

*Framework version:* spring-boot-starter-parent 2.3.8.RELEASE

*Frontend service:* AWS::Serverless::HttpApi (API Gateway HTTP)

*Deployment method:* SAM CLI

## Scenario
Configure a simple HTTP API proxy to Lambda using Spring Boot 2, and be able to route requests that ignore the stage-name.

## Expected behavior
Stage name (which is part of the path by default) is stripped before spring routes/maps to a controller.

## Actual behavior
Getting 404's b/c spring is mapping `/` vs ``; requires my code to be 'stage-name aware'.

## Steps to reproduce
event-source in sam template for AWS::Serverless::Function
```
Events:
BaseAdmin:
Type: HttpApi
Properties:
ApiId: !Ref Api
Method: any
Path: /{proxy+}
PayloadFormatVersion: "1.0"
RouteSettings:
ThrottlingBurstLimit: 100
ThrottlingRateLimit: 100
TimeoutInMillis: 29000
```
api def in sam template:
```
Api:
Type: AWS::Serverless::HttpApi
Properties:
FailOnWarnings: true
StageName: dev
```
lambda handler
```
public class LambdaHandler implements RequestStreamHandler {
private static final SpringBootLambdaContainerHandler HANDLER;

static {
Application.envSetup();
try {
HANDLER = new SpringBootProxyHandlerBuilder().defaultProxy()
.asyncInit()
.springBootApplication(Application.class)
.buildAndInitialize();
} catch (ContainerInitializationException e) {
e.printStackTrace();
throw new RuntimeException(e);
}
// Want to not need the line below uncommented to work!
// HANDLER.stripBasePath(System.getenv("STRIP_BASE_PATH"));
}

@Override
public void handleRequest(InputStream inputStream, OutputStream outputStream, Context context) throws IOException {
HANDLER.proxyStream(inputStream, outputStream, context);
}
}
```
## Full log output
*Paste the full log output from the Lambda function's CloudWatch logs*
`dev` is the stage name; the mapping is for /api/v1
```
DEBUG DispatcherServlet - GET "/dev/api/v1/some/resource", parameters={}
DEBUG DispatcherServlet - Exiting from "ERROR" dispatch, status 404
```

This isn't the worst thing ever...but it's definitely counter-intuitive to me. Would also appreciate any feedback on my solution; I did try some of the config options mentioned on the wiki page, but none of them seemed to do the trick until i found handler.stripBasePath. If there is a way to do this w/o passing in the StageName, that'd be better. Having it work by default would obviously be best.

Commencez par LambdaHandler et sa configuration SpringBootProxyHandlerBuilder, puis comparez le SAM HttpApi StageName et le chemin du proxy indiqués dans l’issue avec le chemin de la requête reçu par Spring Boot. Vérifiez comment handler.stripBasePath est utilisé et rendez le nom du stage inutile par défaut ; le travail est terminé lorsque des requêtes telles que /dev/api/v1/some/resource sont routées vers /api/v1/some/resource sans 404.

Rédigé par le modèle d'indexation à partir du texte de l'issue.