Add new DirectTransfer/Import max file size app settings

What does this MR do and why?

Add 2 new configurable application settings:

• bulk_import_max_file_download_size - Direct Transfer max file size when downloading from source GitLab instance
• max_import_remote_file_size - file-based Import/Export max remote file size when importing from external Object Storage (e.g. AWS S3)

Migration Output

main: == [advisory_lock_connection] object_id: 224360, pg_backend_pid: 64426
main: == 20230726142141 AddMaxFileDownloadSizeToApplicationSettings: migrating ======
main: -- add_column(:application_settings, :bulk_import_max_download_file_size, :integer, {:default=>0})
main:    -> 0.0051s
main: == 20230726142141 AddMaxFileDownloadSizeToApplicationSettings: migrated (0.0122s) 

main: == [advisory_lock_connection] object_id: 224360, pg_backend_pid: 64426
ci: == [advisory_lock_connection] object_id: 224620, pg_backend_pid: 64428
ci: == 20230726142141 AddMaxFileDownloadSizeToApplicationSettings: migrating ======
ci: -- add_column(:application_settings, :bulk_import_max_download_file_size, :integer, {:default=>0})
ci:    -> 0.0035s
ci: == 20230726142141 AddMaxFileDownloadSizeToApplicationSettings: migrated (0.0296s) 

ci: == [advisory_lock_connection] object_id: 224620, pg_backend_pid: 64428
main: == [advisory_lock_connection] object_id: 224860, pg_backend_pid: 64431
main: == 20230727150416 AddMaxImportRemoteFileSizeToApplicationSettings: migrating ==
main: -- add_column(:application_settings, :max_import_remote_file_size, :integer, {:default=>0})
main:    -> 0.0021s
main: == 20230727150416 AddMaxImportRemoteFileSizeToApplicationSettings: migrated (0.0057s) 

main: == [advisory_lock_connection] object_id: 224860, pg_backend_pid: 64431
ci: == [advisory_lock_connection] object_id: 225060, pg_backend_pid: 64433
ci: == 20230727150416 AddMaxImportRemoteFileSizeToApplicationSettings: migrating ==
ci: -- add_column(:application_settings, :max_import_remote_file_size, :integer, {:default=>0})
ci:    -> 0.0021s
ci: == 20230727150416 AddMaxImportRemoteFileSizeToApplicationSettings: migrated (0.0123s) 

ci: == [advisory_lock_connection] object_id: 225060, pg_backend_pid: 64433

Mentions #384976 (closed)

Screenshots or screen recordings

/admin/application_settings/general page

How to set up and validate locally

Numbered steps to set up and validate the change are strongly suggested.

MR acceptance checklist

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