DYNAMIC_STREAM_METADATA should be decoupled from streamSettings

[shanshanzhu]

Reasoning:
DYNAMIC_STREAM_METADATA configuration should be decoupled from streamSettings.

Current behavior:
when DYNAMIC_STREAM_METADATA is set to true, and streamSettings is not set, the _onXVIZTimeslice throws an error for in operator

Expected fix:
We either need to set the default value for streamSettings to {} in constructor, or do a safe check for streamSettings as in the diff.

[shanshanzhu]

@twojtasz couldn't find streetscape on buildkite. Was that disabled?

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