Update scheduled_scans_max_concurrency for self-managed

What does this MR do and why?

Update scheduled_scans_max_concurrency for self-managed as suggested here.

Related to #468944 (closed)

Migrations

db/migrate/20240628203616_update_scheduled_scans_max_concurrency_in_application_settings_for_self_managed.rb

up

main: == 20240628203616 UpdateScheduledScansMaxConcurrencyInApplicationSettingsForSelfManaged: migrating 
main: -- execute("      UPDATE application_settings\n      SET security_policy_scheduled_scans_max_concurrency = 10000\n      WHERE security_policy_scheduled_scans_max_concurrency = 100\n")
main:    -> 0.0029s

down

main: == 20240628203616 UpdateScheduledScansMaxConcurrencyInApplicationSettingsForSelfManaged: reverting 
main: -- execute("UPDATE application_settings SET security_policy_scheduled_scans_max_concurrency = 100")
main:    -> 0.0079s
main: == 20240628203616 UpdateScheduledScansMaxConcurrencyInApplicationSettingsForSelfManaged: reverted (0.0157s)

db/post_migrate/20240703164251_update_scheduled_scans_max_concurrency_default_value.rb

up

main: == 20240703164251 UpdateScheduledScansMaxConcurrencyDefaultValue: migrating ===
main: -- change_column_default(:application_settings, :security_policy_scheduled_scans_max_concurrency, {:from=>100, :to=>10000})
main:    -> 0.1848s
main: == 20240703164251 UpdateScheduledScansMaxConcurrencyDefaultValue: migrated (0.1897s) 

down

main: == [advisory_lock_connection] object_id: 128420, pg_backend_pid: 49415
main: == 20240703164251 UpdateScheduledScansMaxConcurrencyDefaultValue: reverting ===
main: -- change_column_default(:application_settings, :security_policy_scheduled_scans_max_concurrency, {:from=>10000, :to=>100})
main:    -> 0.1925s
main: == 20240703164251 UpdateScheduledScansMaxConcurrencyDefaultValue: reverted (0.2011s) 

MR acceptance checklist

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