Support Apple Silicon in https://carvel.dev/install.sh

**Describe the problem/challenge you have**

https://carvel.dev/install.sh is not supported for m1 mac.
It checks only Darwin or not.

**Describe the solution you'd like**

It should use a result of `uname -m`, and select binaries by the result.

**Anything else you would like to add:**

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We are also happy to receive and review Pull Requests if you want to help working on this issue.

Start with the install.sh script linked in the issue and inspect its current Darwin check and binary-selection logic. Use uname -m as the stated basis for selecting binaries, and consider the work complete when the installer supports Apple Silicon as well as existing macOS architectures.

Written by the indexing model from the issue text.