Guard optional dependencies in try/except blocks

[dagardner-nv]

Description

• Add missing dependencies for requests, requests-cache and websockets to meta.yaml
• Dependencies which are only utilized by a single stage are intentionally omitted from meta.yaml, even if they appear in cuda11.8_dev.yml
• Current that list is: bs4, elasticsearch, feedparser and milvus
• Move MILVUS_DATA_TYPE_MAP from morpheus/service/vdb/milvus_client.py to tests/test_milvus_vector_db_service.py which was the only place it was used.

Note: Since these dependencies all exist in cuda11.8_dev.yml, there is no effort made to update the tests to optionally skip their associated tests.

Closes #1380

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• I am familiar with the Contributing Guidelines.
• When the PR is ready for review, new or existing tests cover these changes.
• When the PR is ready for review, the documentation is up to date with these changes.

[mdemoret-nv]

Have some questions. We can add these dependencies but they arent used in many situations. Can we get by with an import guard instead to instruct the user to install these packages if this particular node type is used?

[mdemoret-nv]

Looks better now. Will eventually need to re-address some of these in #1389

[mdemoret-nv]

/merge