Add incident association flags

[kwent]

Summary

• add incident create/update flags for services, incident types, functionalities, environments, teams, and causes
• accept comma-separated slugs or UUIDs, matching the server friendly-association contract
• serialize each association to the corresponding incident API field
• cover create/update payloads and command wiring with tests

Closes #53

Testing

• go test ./...

[kwent]

@greptileai

[greptile-apps]

Greptile Summary

The PR adds incident association flags for create and update commands and serializes supplied slugs or UUIDs into the corresponding API fields.

• Supports services, incident types, functionalities, environments, teams, and causes.
• Preserves omitted update associations while allowing explicit empty arrays to clear them.
• Adds API payload and command-wiring coverage, including the previously requested omitted-versus-empty update test.

Confidence Score: 5/5

The PR appears safe to merge.

No blocking failure remains.

Important Files Changed

Filename	Overview
internal/api/client.go	Generalizes incident mutation options to support association arrays and forwards the six supported association fields.
internal/cmd/incidents/create.go	Adds create flags for six association types and maps non-empty values into the incident payload.
internal/cmd/incidents/update.go	Adds update association flags while using explicit flag-change detection to distinguish omission from clearing.
internal/cmd/incidents/cmd_test.go	Adds command-level verification that an explicitly empty services flag sends an empty array while an omitted types flag remains absent.
internal/api/client_http_test.go	Extends create-request coverage to verify all association fields are serialized.
internal/api/client_mutations_test.go	Extends update-request coverage to verify all association fields are serialized.

_{Reviews (4): Last reviewed commit: "test clearing incident associations" | Re-trigger Greptile}

[kwent]

@greptileai

[kwent]

@greptileai