Chroma DocumentStore throws error at creation if collection exists

[TuanaCelik]

Describe the bug
When intializing the ChromaDocumentStore, if you rerun the cell without changing the collection name, you will get an error saying telling you collection already exists.

Expected behaviour: Instead of the init calling 'create' by default, if collection already exists, it should simply connect to the existing collection. The current state means we cannot reuse a collection lateron.

To Reproduce
Any colab that has a cell with document_store = ChromaDocumentSrore()
Here is one for example: https://colab.research.google.com/drive/19NzliNb5ZUo1fUbplwnUrZpNBxs9HvoR?usp=sharing

Describe your environment (please complete the following information):

• Integration version: chroma_haystack-0.9.0