feat(set-env-vars): add subject, test and solution for the exercise

sh/tests/set-env-vars_test.sh

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+#!/usr/bin/env bash
+
+# Unofficial Bash Strict Mode
+set -euo pipefail
+IFS='
+'
+
+submitted=$(bash student/set-env-vars.sh)
+expected=$(bash solutions/set-env-vars.sh)
+
+diff <(echo "$submitted") <(echo "$expected")

sh/tests/solutions/set-env-vars.sh

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+#!/usr/bin/env bash
+
+export MY_MESSAGE="Hello World"
+export MY_NUM=100
+export MY_PI=3.142
+export MY_ARR=(one, two, three, four, five)
+printenv

subjects/devops/set-env-vars/README.md

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+## set-env-vars
+
+### Instructions
+
+Create a script `set-env-vars.sh`, which will allow you to set the following variables as environment variables and and print them all:
+
+- `MY_MESSAGE` which contains the string `"Hello World"`.
+- `MY_NUM` which contains the number `100`.
+- `MY_PI` which contains the number `3.142`.
+
+Expected output:
+
+```console
+$ printenv  # The env variables present are just an example, yours will be different.
+SHELL=/bin/bash
+TERM=xterm
+USER=demouser
+LS_COLORS=rs=0:di=01;34:ln=01;36:mh=00:pi=40;33:so=01;35:do=01;35:bd=40;33;01:cd=40;33;01:or=40;31;01:su=37;41:sg=30;43:ca:...
+MAIL=/var/mail/demouser
+PATH=/usr/local/bin:/usr/bin:/bin:/usr/local/games:/usr/games
+PWD=/home/demouser
+LANG=en_US.UTF-8
+SHLVL=1
+HOME=/home/demouser
+LOGNAME=demouser
+LESSOPEN=| /usr/bin/lesspipe %s
+LESSCLOSE=/usr/bin/lesspipe %s %s
+_=/usr/bin/printenv
+$ ./set-env-vars.sh
+MY_NUM=100
+SHELL=/bin/bash
+TERM=xterm
+USER=demouser
+LS_COLORS=rs=0:di=01;34:ln=01;36:mh=00:pi=40;33:so=01;35:do=01;35:bd=40;33;01:cd=40;33;01:or=40;31;01:su=37;41:sg=30;43:ca:...
+MAIL=/var/mail/demouser
+PATH=/usr/local/bin:/usr/bin:/bin:/usr/local/games:/usr/games
+PWD=/home/demouser
+LANG=en_US.UTF-8
+MY_PI=3.142
+SHLVL=1
+HOME=/home/demouser
+LOGNAME=demouser
+MY_MESSAGE=Hello World
+LESSOPEN=| /usr/bin/lesspipe %s
+LESSCLOSE=/usr/bin/lesspipe %s %s
+_=/usr/bin/printenv
+$
+```
+
+### Hints
+
+Setting values to environment variables
+
+In order to set a value to an existing environment variable, we use an assignment expression. For instance, to set the value of the "LANG" variable to "he_IL.UTF-8", we use the following command:
+
+```console
+$ LANG=he_IL.UTF-8
+```
+
+If we use an assignment expression for a variable that doesn't exist, the shell will create a shell variable, which is similar to an environment variable but does not influence the behaviour of other applications.
+
+A shell variable can be exported to become an environment variable with the export command. To create the "EDITOR" environment variable and assign the value "nano" to it, you can do:
+
+```console
+$ EDITOR=nano
+$export EDITOR
+```
+
+> You have to use Man or Google to know more about commands flags, in order to solve this exercise!
+> Google and Man will be your friends!