Add workflow to build wasm simapp

[chatton]

Description

Workflow can be run from main to build the wasm simapp from the specified branch with the specified docker tag.

In the future we can make this automatically build for wasm tags.

Before we can merge this PR, please make sure that all the following items have been
checked off. If any of the checklist items are not applicable, please leave them but
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• Targeted PR against correct branch (see CONTRIBUTING.md).
• Linked to Github issue with discussion and accepted design OR link to spec that describes this work.
• Code follows the module structure standards and Go style guide.
• Wrote unit and integration tests.
• Updated relevant documentation (docs/) or specification (x/<module>/spec/).
• Added relevant godoc comments.
• Provide a commit message to be used for the changelog entry in the PR description for review.
• Re-reviewed Files changed in the Github PR explorer.
• Review Codecov Report in the comment section below once CI passes.

[damiannolan]

quick skim looks good