challenger: Allow interrupting subcommands

[ajsutton]

Description

Support interrupting the execution of challenger sub-commands with ctrl-C. Just uses a very simple Context cancellation which doesn't for managing the shutdown process but that's not required for these subcommands.

Builds on #10757

Metadata

• Fixes https://github.com/ethereum-optimism/client-pod/issues/920

[semgrep-app]

Semgrep found 2 invalid-usage-of-modified-variable findings:

• op-conductor/conductor/service.go
  • L704-721 - Triage
  • L704-721 - Triage

Variable unsafeInNode is likely modified and later used on error. In some cases this could result in panics due to a nil dereference

_{Ignore this finding from invalid-usage-of-modified-variable.}