Assets serial column should have an index

[travismiller]

Server (please complete the following information):

• Snipe-IT: v4.9.3
• OS: Ubuntu 16.04 (Docker)
• Web Server: Apache
• PHP Version: 7.1.33

Is your feature request related to a problem? Please describe.
Importing assets with artisan snipeit:import takes significantly longer when assets have a serial number.

Describe the solution you'd like
Add an index to column assets.serial.

Describe alternatives you've considered
N/A

Additional context

16000 assets without Serial Number
without index: ~6 minutes
with index: ~6 minutes

16000 assets with Serial Number
without index: ~1 hour ⚠️
with index: ~6 minutes

[travismiller]

I’m happy to submit a PR if this suggested solution is acceptable.

[snipe]

Do you have unique serial numbers enabled in your settings?

[travismiller]

Yes, the setting is enabled.

[uberbrady]

We would take a PR that added a non-unique index for serial (some users have duplicated serial numbers for some bizarre reason. We need to support that, unfortunately).