Replace shell LHAPDF installation with Python-based one

It ensures that the tools are available on every platform, since the
script only makes use of Python standard library.
Otherwise it was not even possible to rely on `wget` or `realpath`...

.github/workflows/cli-wheels.yml

@@ -45,11 +45,7 @@ jobs:
           pip install maturin auditwheel
       - name: Install non-Rust dependencies
         run: |
-          for script in {install,download,variables}; do
-            curl -O \
-              https://raw.githubusercontent.com/NNPDF/workflows/v2/packages/lhapdf/${script}.sh
-          done
-          sh install.sh
+          python maintainer/install-lhapdf.py
       - name: Build wheels
         run: |
           # `--find-interpreter` is needed to generate wheels for
@@ -94,11 +90,7 @@ jobs:
           pip install maturin delocate
       - name: Install non-Rust dependencies
         run: |
-          for script in {install,download,variables}; do
-            curl -O \
-              https://raw.githubusercontent.com/NNPDF/workflows/v2/packages/lhapdf/${script}.sh
-          done
-          sh install.sh
+          python maintainer/install-lhapdf.py
       - name: Build wheels
         run: |
           # `--find-interpreter` is needed to generate wheels for
@@ -144,11 +136,7 @@ jobs:
           pip install maturin delvewheel
       - name: Install non-Rust dependencies
         run: |
-          for script in {install,download,variables}; do
-            curl -O \
-              https://raw.githubusercontent.com/NNPDF/workflows/v2/packages/lhapdf/${script}.sh
-          done
-          sh install.sh
+          python maintainer/install-lhapdf.py
       - name: Build wheels
         run: |
           # `--find-interpreter` is needed to generate wheels for