[DOCS] fix openvino_custon_sphinx_sitemap installation (#24536)

### Details:
 - *item1*
 - *...*

### Tickets:
 - *ticket-id*

.github/workflows/build_doc.yml

@@ -39,6 +39,7 @@ jobs:
         run: |
           python3 -m pip install -r docs/requirements.txt
           (cd docs/openvino_sphinx_theme && python3 setup.py install)
+          python3 -m pip install docs/openvino_custom_sphinx_sitemap
 
       - name: Download and install doxygen
         run: |

docs/documentation_build_instructions.md

@@ -21,17 +21,22 @@ $ apt install -y doxygen graphviz texlive
 ```
 $ python3 -m venv env
 $ source env/bin/activate
+(env) $ pip install --upgrade setuptools pip
 (env) $ pip install -r docs/requirements.txt
 ```
 5. Install the sphinx theme
 ```
 (env) $ cd docs/openvino_sphinx_theme && python setup.py install && cd -
 ``````
-6. Create build folder:
+6. Install the custom sphinx sitemap
+```
+(env) $ pip install docs/openvino_custom_sphinx_sitemap
+``````
+7. Create build folder:
 ```
 (env) $ mkdir build && cd build
 ```
-7. Build documentation using these commands:
+8. Build documentation using these commands:
 ```
 (env) $ cmake .. -DENABLE_DOCS=ON
 (env) $ cmake --build . --target sphinx_docs

docs/requirements.txt

@@ -46,5 +46,4 @@ sphinxcontrib-qthelp==1.0.3
 sphinxcontrib-serializinghtml==1.1.9
 toml==0.10.2
 urllib3==1.26.18
-zipp==3.4.1
-docs/openvino_custom_sphinx_sitemap
+zipp==3.4.1