[core] connection string parser only

[swathipil]

This is an attempt to create a generic connection string parsing function that will be used across SDKs to minimize redundant logic and validation, addressing #16782.

Split from PR: #17049

This parsed connection string will be returned as a dict of connection string keys (ie. Endpoint, SharedAccessKey, etc.) and values, with an option for allowing case insensitive keys. This option is useful when checking a connection string with keys that don't match expected case, without looping through all the keys. For example:

conn_str = "Endpoint=XXXXENDPOINT;ACcEsSKEY=XXXXKEY"
parsed = parse_connection_string(conn_str, case_sensitive_keys=False)
endpoint = parsed.get("endpoint")   # value is XXXXENDPOINT
accesskey = parsed.get("accesskey")  # value is XXXXKEY

gist: https://gist.github.com/swathipil/0640998161b2b9fb41dee053e16a770c

[annatisch]

For some reason the documentation for this doesn't seem to be rendering?

[swathipil]

🤔 looking into it!

[swathipil]

I copied the _connection_string_parser.py file to azure/core and imported parse_connection_string in azure/core/__init__.py. The change showed up in the docs, so I don't think _connection_string_parser.py has errors that would cause rendering failure.

I also copied the azure/core/tracing folder to a azure/core/tracing_copy folder and assumed that if tracing is working, then tracing_copy should also render. This didn't work either, so I believe this might not be a problem with the code/the __init__.py file either. Thoughts, @annatisch ?