Support installing Mach nominated zig version

[akhildevelops]

Hi @AMythicDev,

This PR provides below features:

• Install mach nominated zig: zigverm install mach-latest
• zigverm doesn't error out if no args are supplied, instead displays a help message.
• Caches index.json files for both mach and zig that's helpful when updating all versions.

[AMythicDev]

Also I didn't clearly get where you used the Cache. If I missed its usage somewhere, you can point it out to me.

[akhildevelops]

HI @AMythicDev, do you have more concerns ?

[akhildevelops]

There are some issues, will resolve and ping you.

[AMythicDev]

I am fine with the cache. Can you take a look at my leftover concerns?

[AMythicDev]

Any update on this?

[akhildevelops]

@AMythicDev I'm just back from my vacation and currently have other priority works. Closing this PR hanging and will resume when I find time. Thanks