Group routes does not work without leading slash

Group route does not work without leading slash

I ran into an unexpected behavior with grouped routes.

g := e.Group("/v1")
g.GET("posts", handler)

Requesting:

GET /v1/posts

returns:

Not Found

Changing it to:

g.GET("/posts", handler)

works as expected.

I would expect Echo to handle the missing leading / when combining the group prefix and route path, or at least provide a warning during route registration.

It would be nice if both forms resulted in /v1/posts:

g.GET("posts", handler)
g.GET("/posts", handler)

Because it is very normal for a developer to not provide the slash since a group already means it's under that group (so slash should come automatically)

Otherwise its too confusing and something to forget easily when using the framework!!

Start by reproducing the grouped-route example in the issue and trace Echo's group route registration and matching behavior. Add regression coverage for both g.GET("posts", handler) and g.GET("/posts", handler) under /v1; done means requests to /v1/posts resolve in both cases, or the documented warning behavior is covered.