[Cosmos] Adds full text policy and full text indexes

[simorenoh]

This PR adds the functionality, samples and tests for creating and replacing containers with full text policies and full text indexes for the SDK.

A sample full text policy looks like this:

full_text_policy = {
    "defaultLanguage": "en-US",
    "fullTextPaths": [
        {
            "path": "/text",
            "language": "en-US"
        }
    ]
}

For the indexing bit, we now simply accept fullTextIndexes to the existing indexing policy:

indexing_policy = {
    "automatic": True,
    "indexingMode": "consistent",
    "compositeIndexes": [
        [
            {"path": "/numberField", "order": "ascending"},
            {"path": "/stringField", "order": "descending"}
        ]
    ],
    "fullTextIndexes": [
        {"path": "/text"}
    ]
}

[azure-sdk]

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azure-cosmos

[FabianMeiswinkel]

LGTM - but left few comments that need to be addressed before merging.

[FabianMeiswinkel]

LGTM - Thanks!