fix(logs_alert): add Computed to filter_type and incident_settings fields

[lorepanichi]

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Output from acceptance testing:

$ make testacc TEST=./ibm/service/logs TESTARGS='-run=TestAccIbmLogsAlert'

Test failures are pre-existing and unrelated to this change:

summary: 'CreateAlertWithContext failed: ''notification_groups'' field cannot be set for ''new_value'' alerts'

The schema change (adding Computed: true to filter_type and incident_settings fields)
was validated manually via OpenTofu plan/apply — perpetual diff no longer occurs.

Summary

Add Computed: true to filter_type and incident_settings block (and some nested fields) in ibm_logs_alert.

These fields are populated by the API with defaults when not set by the user. Without Computed, Terraform treats API-returned values as drift and plans to remove them on every subsequent apply.