Escape slashes in entity keys when they appear in the URL path

[frij-aws]

Pyodata does not correctly escape the path when an entity key contains a /. This minor correction quotes the entity key with safe="" to ensure slashes are quoted. The rest of the path is quoted with the default (`safe='/') so that path delimiters are not quoted.

Closes #282

[cla-assistant]

All committers have signed the CLA.

[phanak-sap]

Note: if you see the changelog entries, we add also author names for important changes. So feel free to add yourself to this line :)

[frij-aws]

Adding my name for the fame and fortune!

[phanak-sap]

HI @frij-aws

thank you for your work. Generic stuff I commented in the issue, here just what's relevant to the code changes. Nothing existing in the test suite is changed or broken, that's great.

If I may, I would like to ask you to enhance bit the test code.

1. up to consideration for you is whether it would make sense to you to update existing metadata.xml or create new metadata.xml for the test fixtures with these "interesting" entity names. But the new tests are good enough for covering this. If pytest fixtures are not what you work with frequently, ignore this point.
2. however I would like you to also add new test for this entity id case related to batch processing. I do not have service at hand with such $metadata I could test this PR against directly and I am not sure if this fix needs to be applied in the encode_multipart / decode_multipart functions as well. So pls check in the test_service_v2.py test_batch_request and test_batch_request_not_encoded_path and add new one that will cover the expected encoding for your FOO/BAR entity.
3. Is is possible that the FOO/BAR id case is also applicable to the function import names, which are also forming URLs?