fix(signature): realigning SignatureManager with specs #284

Description

Following drift in specs and parallel development, SignatureManager and related elements must be updated to realign between the OpenAEV backend and the OpenAEV injectors.

• The url to be targeted is supposed to be /api/injects/execution/callback/{injectId} instead of /api/injects/{injectId}/callback
• The payload should be aligned with feat(signatures): implement structured output processor behaviour in backend openaev#5447, other sources of truth were out-of-date
  • execution_status moves from a (post-) signature to being part of the POST envelope
  • create relevant execution_action matching Java-side enum from https://github.com/OpenAEV-Platform/openaev/blob/bba8f2f2180f1a789f7be84144bc2562b62b93e6/openaev-api/src/main/java/io/openaev/rest/inject/form/InjectExecutionAction.java#L3
  • (pre-) signature start_time and (post-) signature end_time used to fill execution_duration
  • reintroducing the target metadata in the structured output (feat(injector-common): adding a target meta extractor injectors#274 has been made to assist with that)
• Replace the current chunking method (based on datasize calculations and chunk numbering) with an iterative approach
• Withdraw references to an external injector type (e.g. ExternalInjectorConfig), scope has been refocused around network and cloud

Additional information

This is a follow-up to #206 and #257