gh-pages workflow update to remove archived actions-rs

[zees-dev]

Description

Updated the github pages workflow; switch from actions-rs/toolchain@v1 to dtolnay/rust-toolchain@master for rust env setup.
Also added the wasm32-unknown-unknown target.

Completely removed actions-rs actions - since these are now archived.
Inlined the actions-rs/cargo@v1 to cargo install - since the toolchain/binary is available via dtolnay/rust-toolchain action.

Checklist

• I have linked to any relevant issues.
• I have commented my code, particularly in hard-to-understand areas.
• I have updated the documentation where relevant (API docs, the reference, and the Sway book).
  • If my change requires substantial documentation changes, I have requested support from the DevRel team
• I have added tests that prove my fix is effective or that my feature works.
• I have added (or requested a maintainer to add) the necessary Breaking* or New Feature labels where relevant.
• I have done my best to ensure that my PR adheres to the Fuel Labs Code Review Standards.
• I have requested a review from the relevant team or maintainers.