CI: integrate Poetry for dependency management and update MPM installation instructions in documentation

.github/workflows/custom_build.yml

@@ -138,7 +138,8 @@ jobs:
       - name: Install Python Requirements
         working-directory: firmware
         run: |
-          python -m pip install -r requirements.txt -t pyvendor
+          pip install poetry
+          poetry install
 
       - name: Update Status - Installing plugins
         if: ${{ inputs.plugins != '' }}
@@ -151,7 +152,7 @@ jobs:
         if: ${{ inputs.plugins != '' }}
         working-directory: firmware
         run: |
-          python ./bin/mpm_pio.py install ${{ inputs.plugins }}
+          poetry run mpm install ${{ inputs.plugins }}
 
       - name: Update Status - Downloading PlatformIO Cache
         shell: bash