Move NPM build step inside of client variant logic inside of build_example

[jul-sh]

Checklist

• Pull request affects core Oak functionality (e.g. runtime, SDK, ABI)
  • I have written tests that cover the code changes.
  • I have checked that these tests are run by
    Cloudbuild
  • I have updated documentation accordingly.
  • I have raised an issue to
    cover any TODOs and/or unfinished work.
• Pull request includes prototype/experimental work that is under
  construction.

[jul-sh]

@anghelcovici

Thanks for your comment! Most of the code in this draft PR (the first commit) actually was PR'ed in #1170 & merged earlier.

I left this PR in draft as further work, but it's not fully ready yet. The aspect this PR will address specifically is into the client variant in the build_example step. :)

[github-actions]

Reproducibility Index:

e1c5b8b551b683e7c3c12346ba65dad9ab184abac9d59d3c605ae5a7a5aa7895  ./examples/target/wasm32-unknown-unknown/release/abitest_0_frontend.wasm
e89bb8621965e356156c939997a61fa1af30352159ae9e7a59f50a8eb101648d  ./examples/target/wasm32-unknown-unknown/release/abitest_1_backend.wasm
b256b1c1402a8f25381352047ee48cc9a07314d4227a64bd786369a17c61d1df  ./examples/target/wasm32-unknown-unknown/release/aggregator.wasm
44eff10ce70a232c84cc32c225e75eca695634abc9ecfbf543022aa0a5682cd7  ./examples/target/wasm32-unknown-unknown/release/chat.wasm
b28dc802af588ea6512974d2d9ec17557dd454f760b379ab80b11efbe444ecfd  ./examples/target/wasm32-unknown-unknown/release/hello_world.wasm
1123ddd109dd00155b0f59ccc2f3025974bacc82e15a4d1fe2a83ff6ceb2b3cd  ./examples/target/wasm32-unknown-unknown/release/machine_learning.wasm
66ae9e10c2d72cab7e629b2fea2ae98939649c391480ab255d589f5da8c7ae0f  ./examples/target/wasm32-unknown-unknown/release/private_set_intersection.wasm
0cd8cb0baae0c59852e775a697ca5408f975c1c1fdc53cc8f3a0e7d07e23f5af  ./examples/target/wasm32-unknown-unknown/release/running_average.wasm
15da62b4701e02ae731276dbe8bdfd29805871e7f863e8e15b1fe11983023159  ./examples/target/wasm32-unknown-unknown/release/translator.wasm
571d966c66ebf487d1f07ae0aba89fe22bcf8d09fcd861a490aec215c4b94aa9  ./examples/target/wasm32-unknown-unknown/release/trusted_information_retrieval.wasm
316d402713bec5c83d5583e21aa73b1b4f36a7d3be4e96cd0759c93a8bcb2ae0  ./oak/server/target/x86_64-unknown-linux-musl/release/oak_loader

Reproducibility Index diff: