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?

Tasklist

• Add test case(s)
• Add documentation
• Updated Python API documentation (swig/include/python/docs/)
• Review
• Adjust for comments
• All CI builds and checks have passed

[kssvrk]

This pull request has non standard documentation , i am sorry for the PR.
Just deployed the documentation and checked. Will submit another PR shortly. Closing this request.

First time contributor for gdal :)