fix: avoid error for missing image if pod is provided

[kurokobo]

Closes #712

Tested this PR in various patterns:

# Fixed: Case that previously resulted in an error as #712
$ ./receptor --local-only --work-kubernetes worktype=demo allowruntimeauth=true pod=/tmp/pod.yml
INFO 2022/12/24 09:03:25 Initialization complete

# Invalid configuration; resulted expected error
$ ./receptor --local-only --work-kubernetes worktype=demo allowruntimeauth=true
Error: must specify a container image to run

$ ./receptor --local-only --work-kubernetes worktype=demo allowruntimeauth=true pod=/tmp/pod.yml image=busybox
Error: can only provide Pod when Image, Command, and Params are empty

$ ./receptor --local-only --work-kubernetes worktype=demo allowruntimeauth=true pod=/tmp/pod.yml command=sleep
Error: can only provide Pod when Image, Command, and Params are empty

$ ./receptor --local-only --work-kubernetes worktype=demo allowruntimeauth=true pod=/tmp/pod.yml params=10
Error: can only provide Pod when Image, Command, and Params are empty

# Valid configuration
$ ./receptor --local-only --work-kubernetes worktype=demo allowruntimeauth=true allowruntimecommand=true
INFO 2022/12/24 09:04:00 Initialization complete

$ ./receptor --local-only --work-kubernetes worktype=demo allowruntimeauth=true allowruntimepod=true
INFO 2022/12/24 09:04:02 Initialization complete

$ ./receptor --local-only --work-kubernetes worktype=demo allowruntimeauth=true image=busybox
INFO 2022/12/24 09:04:06 Initialization complete

$ ./receptor --local-only --work-kubernetes worktype=demo allowruntimeauth=true image=busybox allowruntimecommand=true
INFO 2022/12/24 09:04:08 Initialization complete

$ ./receptor --local-only --work-kubernetes worktype=demo allowruntimeauth=true image=busybox allowruntimepod=true
INFO 2022/12/24 09:04:10 Initialization complete

[kurokobo]

CI / receptor (Go 1.19) (pull_request) failed but seems caused by unrelated to the changes made in this PR.

2023-02-02T15:29:43.2907411Z netceptor_test.go:478: timed out waiting for duplicate node to terminate
2023-02-02T15:29:43.2908761Z --- FAIL: TestDuplicateNodeDetection (121.64s)
...
2023-02-02T15:29:49.2362466Z FAIL
2023-02-02T15:29:49.2363079Z FAIL github.com/ansible/receptor/pkg/netceptor 129.570s

2023-02-02T15:30:00.5404997Z --- FAIL: TestNegativeCost (0.07s)
2023-02-02T15:30:00.5405600Z --- PASS: TestNegativeCost/--tcp-listener (0.13s)
2023-02-02T15:30:00.5406130Z --- PASS: TestNegativeCost/--udp-listener (0.22s)
2023-02-02T15:30:00.5406666Z --- FAIL: TestNegativeCost/--ws-listener (0.24s)
...
2023-02-02T15:30:02.3588954Z FAIL
2023-02-02T15:30:02.3611663Z FAIL github.com/ansible/receptor/tests/functional/cli 2.212s

[AaronH88]

Hey @kurokobo , with all the tests updated im sure this PR will pass our checks now.
Would you like to rebase, or shall I do it?

[kurokobo]

@AaronH88
Thanks for updating, I've rebased and force-pushed 😃

[AaronH88]

lgtm