Eigenlayer cli install script

[shrimalmadhur]

Is your feature request related to a problem? Please describe.
Currently when we release a new version of eigenlayer-cli, we need to update the readme page to reflect that version change - like this PR - #128

We want to create an install script which can just always get the latest release based on OS.
One example is - https://github.com/coinbase/rosetta-cli/blob/master/scripts/install.sh

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