Add the framework and mocks for testing udp_proxy.go #3408

Job	Run time
lint-receptor	21s
lint-receptor	21s
receptor (Go 1.20)	4m 10s
receptor (Go 1.20)	4m 10s
container	2m 43s
container	2m 43s
receptor (Go 1.21)	6m 40s
receptor (Go 1.21)	6m 40s
Lint receptorctl / Run `receptorctl` check_style session	14s
Lint receptorctl / Run `receptorctl` check_style session	14s
Lint receptorctl / Run `receptorctl` check_format session	16s
Lint receptorctl / Run `receptorctl` check_format session	16s
Receptorctl test coverage (coverage)	1m 10s
Receptorctl test coverage (coverage)	1m 18s
Run receptorctl tests / Run `receptorctl` tests-3.10 session	1m 11s
Run receptorctl tests / Run `receptorctl` tests-3.10 session	1m 11s
Run receptorctl tests / Run `receptorctl` tests-3.11 session	59s
Run receptorctl tests / Run `receptorctl` tests-3.11 session	59s
Run receptorctl tests / Run `receptorctl` tests-3.12 session	1m 3s
Run receptorctl tests / Run `receptorctl` tests-3.12 session	1m 3s
Run receptorctl tests / Run `receptorctl` tests-3.8 session	1m 19s
Run receptorctl tests / Run `receptorctl` tests-3.8 session	1m 19s
Run receptorctl tests / Run `receptorctl` tests-3.9 session	1m 18s
Run receptorctl tests / Run `receptorctl` tests-3.9 session	1m 18s
	42m 56s

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