docs: `disk_size`

[tenthirtyam]

Summary

• Clarifies that disk_size in the vsphere-clone builder only supports a single disk.
• Adds a TODO note for future enhancements to findDisk and ResizeDisk functions.

Tessting

packer-plugin-vsphere1 on  docs/disk-size-usage via 🐹 v1.22.2 
➜ make generate
2024/04/18 21:14:24 Copying "docs" to ".docs/"
2024/04/18 21:14:24 Replacing @include '...' calls in .docs/
Compiling MDX docs in '.docs' to Markdown in '.web-docs'...

packer-plugin-vsphere1 on  docs/disk-size-usage via 🐹 v1.22.2 took 12.5s 
➜ make build   

packer-plugin-vsphere1 on  docs/disk-size-usage via 🐹 v1.22.2 took 5.2s 
➜ make test
?       github.com/hashicorp/packer-plugin-vsphere      [no test files]
?       github.com/hashicorp/packer-plugin-vsphere/builder/vsphere/common/testing       [no test files]
?       github.com/hashicorp/packer-plugin-vsphere/builder/vsphere/examples/driver      [no test files]
?       github.com/hashicorp/packer-plugin-vsphere/version      [no test files]
ok      github.com/hashicorp/packer-plugin-vsphere/builder/vsphere/clone        1.908s
ok      github.com/hashicorp/packer-plugin-vsphere/builder/vsphere/common       2.869s
ok      github.com/hashicorp/packer-plugin-vsphere/builder/vsphere/driver       5.798s
ok      github.com/hashicorp/packer-plugin-vsphere/builder/vsphere/iso  1.466s
ok      github.com/hashicorp/packer-plugin-vsphere/builder/vsphere/supervisor   4.109s
ok      github.com/hashicorp/packer-plugin-vsphere/post-processor/vsphere       2.307s
ok      github.com/hashicorp/packer-plugin-vsphere/post-processor/vsphere-template      2.693s

packer-plugin-vsphere1 on  docs/disk-size-usage via 🐹 v1.22.2 took 8.4s 

Reference

Closes #303