Upgrade to using math/rand/v2 to get perf enhancements

[arvindbr8]

Follow up from: #7283 (comment)

Go1.22 introduced a new rand package with a lot of improvements. See: go.dev/blog/randv2.

We would love to update our usages of math/rand once gRPC-go requires Go 1.22 or later.

[silaselisha]

@arvindbr8 I would like to be assigned this task.

[purnesh42H]

@silaselisha assigned it to you

[easwars]

This is blocked until we bump the minimum Go version supported to 1.22 in our go.mod.

[marcoferrer]

Is switching to randv2 still blocked?

[easwars]

I see that we bumped up our minimum supported Go version to 1.22.7 in #7624. So, this should be unblocked.

@marcoferrer : Would you be interested in making this change? We'll be happy to review. Thanks.