Add support for boot_mode option for Amazon EBS builder

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#### Description

Those PRs #131 and #340 add support for boot_mode, but only for the "Chroot" and "EBS Surrogate" builders.
I would need to be able to select the boot_mode also for "EBS" builder.

#### Use Case(s)

[CIS hardening](https://www.tenable.com/audits/items/CIS_Debian_Linux_10_v1.0.0_L2_Server.audit:2670236182e11f7e8a5d7fd74048994b) needs to disable vfat filesystem. However, as mentionned:
> Disabling the vfat module can prevent boot on UEFI systems.

I'd like to test it out by creating an AMI while booting with Legacy-bios instead of UEFI.

#### Potential configuration

Same as documented on the [EBS Surrogate builder documentation](https://developer.hashicorp.com/packer/integrations/hashicorp/amazon/latest/components/builder/ebssurrogate) for `boot_mode` and optionnaly for `uefi_data`.
Valid options should be `legacy-bios` and `uefi` + the non-mentionned `uefi-preferred` from #362.

#### Potential References
- #131
- #340
- #362
- AWS documentation: https://docs.aws.amazon.com/AWSEC2/latest/UserGuide/ami-boot.html