govc: Add envbrowser query commands

[akutz]

Description

Add a cli/envbrowser package with three govc commands that wrap the vSphere EnvironmentBrowser managed object API:

• envbrowser.query-config-option: query VM hardware config options by hardware version and/or guest ID; supports iterating all known hardware versions (VMX-10+)
• envbrowser.query-config-option-descriptor: list available config option descriptor keys
• envbrowser.query-config-target: query the config target for a host or cluster

All commands accept -host/-cluster to select the compute object and -copy-to-file to serialize the result as XML.

The directory cli/envbrowser/testdata also includes examples of all of the output from each command when using the -copy-to-file flag.

Closes: NA

How Has This Been Tested?

By running the commands against a real vSphere instance. I will update this PR with tests against vC Sim.

Guidelines

Please read and follow the CONTRIBUTION guidelines of this project.

[dougm]

I haven't looked close yet, sounds similar to these existing commands that use the same Envbrowser methods?

https://github.com/vmware/govmomi/blob/main/govc/USAGE.md#vmoptioninfo
https://github.com/vmware/govmomi/blob/main/govc/USAGE.md#vmoptionls
https://github.com/vmware/govmomi/blob/main/govc/USAGE.md#vmtargetinfo

[akutz]

I haven't looked close yet, sounds similar to these existing commands that use the same Envbrowser methods?

https://github.com/vmware/govmomi/blob/main/govc/USAGE.md#vmoptioninfo https://github.com/vmware/govmomi/blob/main/govc/USAGE.md#vmoptionls https://github.com/vmware/govmomi/blob/main/govc/USAGE.md#vmtargetinfo

Dammit 😁

I looked for an existing command, but missed this somehow. Thanks @dougm . Let me see if I did anything novel, and if I did, if I can fold it into the existing command.