(Icons): updated tether icon + added tether gold XAUT one

[LFBarreto]

Context (issues, jira)

update tether icon

Description / Usage

Expectations

• Test coverage: The changes of this PR are covered by test. Unit test were added with mocks when depending on a backend/device.
• No impact: The changes of this PR have ZERO impact on the userland. Meaning, we can use these changes without modifying LLD/LLM at all. It will be a "noop" and the maintainers will be able to bump it without changing anything.

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