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

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)