feat: create bash install script

[leodido]

Fixes #115
Supersedes #116

How to

# binary will be $(go env GOPATH)/bin/lstn
curl -sSfL https://raw.githubusercontent.com/listendev/lstn/main/install.sh | sh -s -- -b $(go env GOPATH)/bin 

# or install it into ./bin
curl -sSfL https://raw.githubusercontent.com/listendev/lstn/main/install.sh | sh -s 

# in Alpine Linux (as it does not come with curl by default)
wget -O- -nv https://raw.githubusercontent.com/listendev/lstn/main/install.sh | sh -s 

Notice: change main to feat/install-script until this is merged in.

What's missing?

Signature verification.

For future reference here's how to verify the signatures:

COSIGN_EXPERIMENTAL=1 cosign verify-blob \
  --certificate ~/Downloads/lstn_0.1.0_macos_amd64.pem \
  --signature ~/Downloads/lstn_0.1.0_macos_amd64.tar.gz.sig \
  ~/Downloads/lstn_0.1.0_macos_amd64.tar.gz
# tlog entry verified with uuid: c8ba1bff17bee82890986cf9c1c867f6989b1a5b7454f828f3d3713049e34ede index: 14006913
# Verified OK

See #118 for further details.

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• I have followed the coding guidelines
• I have written unit tests
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