Add Docker/devcontainer files.

[lucasaf04]

Closes #100

Build log:

Setting up EMSDK environment (suppress these messages with EMSDK_QUIET=1)
Setting environment variables:
PATH = /emsdk:/emsdk/upstream/emscripten:/emsdk/node/18.20.3_64bit/bin:/vscode/vscode-server/bin/linux-arm64/ea1445cc7016315d0f5728f8e8b12a45dc0a7286/bin/remote-cli:/opt/devkitpro/tools/bin:/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin
root@de1a7e87ae8a:/workspaces/uLaunch# make > build_log.txt
fatal: ref HEAD is not a symbolic ref
fatal: ref HEAD is not a symbolic ref
In file included from /workspaces/uLaunch/libs/uCommon/../zip/src/zip.c:37:
/workspaces/uLaunch/libs/uCommon/../zip/src/miniz.h:5106:9: note: '#pragma message: Using fopen, ftello, fseeko, stat() etc. path for file I/O - this path may not support large files.'
 5106 | #pragma message(                                                               \
      |         ^~~~~~~
/opt/devkitpro/devkitA64/bin/../lib/gcc/aarch64-none-elf/14.1.0/../../../../aarch64-none-elf/bin/ld: warning: -z relro ignored
lto-wrapper: warning: using serial compilation of 2 LTRANS jobs
lto-wrapper: note: see the '-flto' option documentation for more information
Failed to get system_resource_size (field not present).
Failed to get version (field not present).
Failed to get process_category (field not present).
Failed to get optimize_memory_allocation (field not present).
Failed to get disable_device_address_space_merge (field not present).
Failed to get signature_key_generation (field not present).
Failed to get system_resource_size (field not present).
Failed to get version (field not present).
Failed to get process_category (field not present).
Failed to get optimize_memory_allocation (field not present).
Failed to get disable_device_address_space_merge (field not present).
Failed to get signature_key_generation (field not present).
Failed to get system_resource_size (field not present).
Failed to get version (field not present).
Failed to get process_category (field not present).
Failed to get optimize_memory_allocation (field not present).
Failed to get disable_device_address_space_merge (field not present).
Failed to get signature_key_generation (field not present).
Failed to get system_resource_size (field not present).
Failed to get version (field not present).
Failed to get process_category (field not present).
Failed to get optimize_memory_allocation (field not present).
Failed to get disable_device_address_space_merge (field not present).
Failed to get signature_key_generation (field not present).
shared:INFO: (Emscripten: Running sanity checks)
In file included from /workspaces/uLaunch/projects/uDesigner/../../libs/zip/src/zip.c:37:
/workspaces/uLaunch/projects/uDesigner/../../libs/zip/src/miniz.h:5106:9: warning: Using fopen, ftello, fseeko, stat() etc. path for file I/O - this path may not support large files. [-W#pragma-messages]
 5106 | #pragma message(                                                               \
      |         ^
1 warning generated.
cache:INFO: generating system asset: symbol_lists/83345a4e65e43ed07ac88b9b4e245f116d70229e.json... (this will be cached in "/emsdk/upstream/emscripten/cache/symbol_lists/83345a4e65e43ed07ac88b9b4e245f116d70229e.json" for subsequent builds)
cache:INFO:  - ok
root@de1a7e87ae8a:/workspaces/uLaunch# 

build_log.txt

Both python (2.7) and python3 are included in the devkitpro/devkita64 image with python-is-python2 installed. I've replaced it with python-is-python3 like you did in GitHub Workflows.