Install Hex and Rebar per OTP release (Elixir v1.18)

[wojtekmach]

Back port of #14477

[wojtekmach]

there's potentially one thing left, lmk if I should re-build Hex 2.x.y against all OTP versions. Maybe let's not, until someone asks for it?

$ mix local.hex --force
* creating .mix/archives/hex-2.2.1-otp-27
$ mix local.hex 2.2.1 --force
* creating .mix/archives/hex-2.2.1-otp-27
$ mix local.hex 2.2.0 --force
** (Mix) Could not find a version of Hex matching: 2.2.0
~/src/elixir[wm-hex-per-otp-release-1.18]$ curl https://builds.hex.pm/installs/hex.csv
2.2.1,29e1c6cd122d7bd3eef0d053420c291328e295834d3b8cbd55f0ac59a818ecd15a94ca676ea42c3a20c7a978aa0b20e7cb71ff481bb7e8127dd9ada769247e74,1.17.0,25
2.2.1,f4e0a635992a7d59da249b40ce94cc9b48708ba0e667212c72137ef009be4d9b45f87fdb76b6ddd758da955e8395541af9b7f19a806515814b15749b3280e207,1.17.0,26
2.2.1,1509ea60bdaa3ca22934f901869bd07bc1f86c6681013287f5dea82a961708d01fb5b4b1b0a8c996fd7d778105f6a6427b8b26e0049ae3025dbd2d6d6aa8f4d1,1.17.0,27
2.2.1,2b72f4762fcfa02762727e96089174a3620f734c9180956d64feedaa7cd4a2e5161039f9869a8e02ac28b70e6c23011bae6eb88aff17ace849f8a333b86c62c7,1.18.0,25
2.2.1,8f50eeb1c953ea1b37ed5f6d0ae985cea81763db75bd4539abad969cf08769d86b1009d14bb8a5d3e62a11c69916d17896965e7d195f76318b0656674b87cb76,1.18.0,26
2.2.1,00bc7eadc097c3293ea106f5eb4366fad6005e2c23bb851bed2e5a4507e8441e07aac1a0c1120b013e24c5daf907b27ab3727b3de03fed45a78dca6ed51e898d,1.18.0,27

[josevalim]

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