Create Github Codespace config for beginners

[trdthg]

Privide a ready-make config for GitHub codespace, this could help beginners participate in ACT.

• This can help them immediately start their work, like running a "hello world" of riscof
• unified-db already has it: Add support for GitHub codespace users riscv-software-src/riscv-unified-db#180
• help people like me: Need help on coverage mode test #542 (comment)
• help people like this: A-extension tests #293 (comment)

Some points that need to be considered:

• sail-model currently has no pre-built files (I haven't found it yet) available for download, building it in codespace (default using 2c 8g) is not very fast
  • make -j$(nproc) 709.97s user 73.81s system 103% cpu 12:34.03 total
• Considering the previous situation of running tests locally, the performance of codespace by default may not be sufficient? I haven't yet calculated how long it takes to run all the coverage.
  • here is the time taken to run basic RV64I: 39.21s user 1.63s system 9% cpu 7:00.56 total

    time riscof coverage --config=config.ini --suite=riscv-arch-test/riscv-test-suite/ --env=riscv-arch-test/riscv-test-suite/env \
      --cgf-file=./riscv-arch-test/coverage/dataset.cgf \
      --cgf-file=./riscv-arch-test/coverage/i/rv64i.cgf \
      --cgf-file=./riscv-arch-test/coverage/priv/rv64i_priv.cgf

• riscv-gnu-toolchain (both rv64 and rv32) can be download from https://github.com/riscv-collab/riscv-gnu-toolchain/releases (because apt only provide rv64)

Even if the performance is really insufficient, users can switch to local Docker for development, and VSCode has very good support for this, consistent with the Codespace experience. So I don't think performance is an big problem

Originally posted by @trdthg in #542 (comment)

[trdthg]

sail-model currently has no pre-built files

I've asked this at the-golden-model metting 11/25. Carl said that He has been doing related work and I' not sure if this overlaps with it.
But what he has done seems to far exceed what I had in mind

More details: https://lists.riscv.org/g/tech-golden-model/topic/target_operating_systems_for/109776300