LambdaRequest lifetime fix

[jelmansouri]

Description of changes:

Making the LambdaHandler implementation for the adapter more generic over the lifetime of the LambdaRequest, issue encountered in valid code yielding such errors:

= note: `lambda_runtime::Handler<lambda_http::request::LambdaRequest<'1>, lambda_http::response::LambdaResponse>` would have to be implemented for the type `lambda_http::Adapter<'0, grpc::aws_lambda_handler::AwsLambdaHandler<tonic_web::service::GrpcWeb<MultiplexerService>>>`, for any two lifetimes `'0` and 
`'1`...
= note: ...but `lambda_runtime::Handler<lambda_http::request::LambdaRequest<'2>, lambda_http::response::LambdaResponse>` is actually implemented for the type `lambda_http::Adapter<'2, grpc::aws_lambda_handler::AwsLambdaHandler<tonic_web::service::GrpcWeb<MultiplexerService>>>`, for some specific lifetime `'2`

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[coltonweaver]

LGTM, thanks for making this fix!