Promoting ogr_layer_algebra to official python script

[kssvrk]

What does this PR do?

This PR Promotes ogr_layer_algebra.py to official Python script mentioned at issue 1581.

What i have done is the following.

• move ogr_layer_algebra.py from swig/python/gdal-utils/osgeo_utils/samples to swig/python/gdal-utils/osgeo_utils/
• create a calling gdal-utils script for ogr_layer_algebra.py in swig/python/gdal-utils/scripts
• Change the arguments of main function of ogr_layer_algebra from argv=None to argv=sys.argv
• created documentation for ogr_layer_algebra at doc/source/programs/
• Linked the documentation for ogr_layer_algebra in index under vector section
• Created test cases for all modes of ogr_layer_algebra at autotest/pyscripts/test_ogr_layer_algebra.py

What are related issues/pull requests?

Tries to solve Issue 1581.

Tasklist

• Reorganised the script
• Add test case
• Add documentation

[rouault]

(please don't close the pull request each time continuous integration raises error. you can just add new commits to fix issues and push again your branch)

could you do the following documented in https://github.com/OSGeo/gdal/blob/master/CONTRIBUTING.md#build-gdal-cmake:
Setup pre-commit (to be done just once):

python -m pip install pre-commit
pre-commit install

and then you can automatically fix the .py files with: pre-commit --run-all -a (this is also automatically done on modified un-committed files when running git commit)

[kssvrk]

@rouault I have done the required changes with pre-commit hook.
black,flake8,isort have passed.
pytest is also succesful for the test script written.
Please let me know if i have to look into anything else.

[kssvrk]

@rouault I have done the recommended changes by you. Kindly review and provide feedback.