Allow `if` Blocks in steps

[fchorney]

Describe the enhancement
I'm finding that it is quite annoying to have to define an if condition for every single item in the steps section of a test matrix. It would be great if you could define a block per se

Code Snippet
For instance, let's say I have a setup like so

 # Linux
 - name: Wait / Sleep
 uses: jakejarvis/wait-action@v0.1.0
 if: ${{ runner.os == 'Linux' }}
 with:
 time: '1m'
 - name: Collect Docker Logs
 uses: jwalton/gh-docker-logs@v1.0.0
 if: ${{ runner.os == 'Linux' }}
 - name: Check running containers
 run: docker ps -a
 if: ${{ runner.os == 'Linux' }}
 - name: Set PGHOST on Linux
 run: echo "PGHOST=localhost" >> $GITHUB_ENV
 if: ${{ runner.os == 'Linux' }}
 # MacOS
 - name: Set PGUSER on macOS
 run: |
 echo "PGUSER=$USER" >> $GITHUB_ENV
 echo "LIBPQJL_DATABASE_USER=$USER" >> $GITHUB_ENV
 if: ${{ runner.os == 'macOS' }}
 - name: Start Homebrew PostgreSQL service
 run: pg_ctl -D /usr/local/var/postgres start
 if: ${{ runner.os == 'macOS' }}
 # Windows
 - name: Add PostgreSQL to Path
 run: |
 echo $env:PGBIN
 echo $env:PGBIN | Out-File -FilePath $env:GITHUB_PATH -Encoding utf8 -Append
 if: ${{ runner.os == 'Windows' }}
 - name: Start Windows PostgreSQL service
 run: |
 pg_ctl -D $env:PGDATA start
 pg_ctl -D $env:PGDATA status
 if: ${{ runner.os == 'Windows' }}

It would be awesome if it could be formatted like so:

 # Linux
 - if: ${{ runner.os == 'Linux' }}
 - name: Wait / Sleep
 uses: jakejarvis/wait-action@v0.1.0
 with:
 time: '1m'
 - name: Collect Docker Logs
 uses: jwalton/gh-docker-logs@v1.0.0
 - name: Check running containers
 run: docker ps -a
 - name: Set PGHOST on Linux
 run: echo "PGHOST=localhost" >> $GITHUB_ENV
 # MacOS
 - if: ${{ runner.os == 'macOS' }}
 - name: Set PGUSER on macOS
 run: |
 echo "PGUSER=$USER" >> $GITHUB_ENV
 echo "LIBPQJL_DATABASE_USER=$USER" >> $GITHUB_ENV
 - name: Start Homebrew PostgreSQL service
 run: pg_ctl -D /usr/local/var/postgres start
 # Windows
 - if: ${{ runner.os == 'Windows' }}
 - name: Add PostgreSQL to Path
 run: |
 echo $env:PGBIN
 echo $env:PGBIN | Out-File -FilePath $env:GITHUB_PATH -Encoding utf8 -Append
 - name: Start Windows PostgreSQL service
 run: |
 pg_ctl -D $env:PGDATA start
 pg_ctl -D $env:PGDATA status