fix: error when using a custom index for map that includes more than two word

[lumtis]

The rpc query path used a wrong naming convention for the index name by setting all characters to lowercase.
For example running starport s map foo --index fooBar fails

We set it to lower camel case so it can correctly retrieve the field in the type.

We also add a test to include this case.

[fadeev]

Looks good!

service Query {
	// Queries a foo by index.
	rpc Foo(QueryGetFooRequest) returns (QueryGetFooResponse) {
		option (google.api.http).get = "/cosmonaut/mars/mars/foo/{fooBar}";
	}
	//...
}