TUN-8861: Add session limiter to UDP session manager

## Summary
In order to make cloudflared behavior more predictable and
prevent an exhaustion of resources, we have decided to add
session limits that can be configured by the user. This first
commit introduces the session limiter and adds it to the UDP
handling path. For now the limiter is set to run only in
unlimited mode.

README.md

@@ -67,6 +67,7 @@ For example, as of January 2023 Cloudflare will support cloudflared version 2023
   - [capnpc-go](https://pkg.go.dev/zombiezen.com/go/capnproto2/capnpc-go)
   - [goimports](https://pkg.go.dev/golang.org/x/tools/cmd/goimports)
   - [golangci-lint](https://github.com/golangci/golangci-lint)
+  - [gomocks](https://pkg.go.dev/go.uber.org/mock)
 
 ### Build
 To build cloudflared locally run `make cloudflared`
@@ -76,3 +77,6 @@ To locally run the tests run `make test`
 
 ### Linting
 To format the code and keep a good code quality use `make fmt` and `make lint`
+
+### Mocks
+After changes on interfaces you might need to regenerate the mocks, so run `make mock`