Add dual integration tests to SNX test suite

[K-Ho]

Description
Adds "dual" integration tests (deposits and withdraws) to the external SNX test suite workflow

Fixes OP-1128

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[tynes]

Will be good to merge once we see it pass here: https://github.com/ethereum-optimism/optimism/actions/runs/1023991800

[tynes]

It ran out of memory, I think this needs to be split up into different tasks that run after each other

[K-Ho]

It ran out of memory, I think this needs to be split up into different tasks that run after each other

looked like it didn't even get past spinning the Optimism stack up, re-running now

[tynes]

@K-Ho - Is this still useful?

[tynes]

@K-Ho Could you provide an update that includes:
1 - how to take advantage of this functionality?
2 - is this still useful?

[tynes]

@K-Ho Any updates on this?

[K-Ho]

@elenadimitrova is taking this over - she was getting issues running these tests (as was I) and is debugging with Synthetix in their discord