Remove support for newly_detected vulnerability status

What does this MR do and why?

This MR removes the support for newly_detected vulnerability status for scan_result_policies

Migrations

approval_project_rules

Up

main: == 20240205171942 ChangeApprovalProjectRulesVulnerabilityStatesDefault: migrating 
main: -- change_column_default("approval_project_rules", "vulnerability_states", {:from=>["newly_detected"], :to=>["new_needs_triage", "new_dismissed"]})
main:    -> 0.0282s
main: == 20240205171942 ChangeApprovalProjectRulesVulnerabilityStatesDefault: migrated (0.0322s) 

Down

main: == 20240205171942 ChangeApprovalProjectRulesVulnerabilityStatesDefault: reverting 
main: -- change_column_default("approval_project_rules", "vulnerability_states", {:from=>["new_needs_triage", "new_dismissed"], :to=>["newly_detected"]})
main:    -> 0.0175s
main: == 20240205171942 ChangeApprovalProjectRulesVulnerabilityStatesDefault: reverted (0.0213s) 

approval_merge_request_rules

Up

main: == 20240205170838 ChangeApprovalMergeRequestRulesVulnerabilityStatesDefault: migrating 
main: -- change_column_default("approval_merge_request_rules", "vulnerability_states", {:from=>["newly_detected"], :to=>["new_needs_triage", "new_dismissed"]})
main:    -> 0.0203s
main: == 20240205170838 ChangeApprovalMergeRequestRulesVulnerabilityStatesDefault: migrated (0.0292s) 

Down

main: == 20240205170838 ChangeApprovalMergeRequestRulesVulnerabilityStatesDefault: reverting 
main: -- change_column_default("approval_merge_request_rules", "vulnerability_states", {:from=>["new_needs_triage", "new_dismissed"], :to=>["newly_detected"]})
main:    -> 0.0181s
main: == 20240205170838 ChangeApprovalMergeRequestRulesVulnerabilityStatesDefault: reverted (0.0218s) 

As described here we want to have MR ready in %16.9 and prepared to be merged in %17.0.

Related to: #422414

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