Fixes for new Go binaries in v0.12.0

Fixes

• Fix pip in py3_image (#1244)
• update bazel-toolchains and fix reference to exec_propertiers: (#1238)
• Added Documentation for container_layer for empty_dirs (#1237)
• Add new adopter (#1236)
• Update dependency io_bazel_rules_go to v0.20.1 (#1234)
• Update rules_python commit hash to f46e953 (#1233)
• Update io_bazel_rules_scala commit hash to 0f89c21 (#1232)
• update go containerregistry (#1230)
• Make pusher emit error if client config is not a valid directory (#1229)
• Fixes for python use in download_pkgs (#1226)
• Update go-containerregistry to fix panic in image tarball writer (#1225)
• Support timeout in Go puller & add test (#1222)
• Support timeout in puller binary (#1221)
• Fix reference to //platforms to include @io_bazel_rules_docker (#1218)
• Update dependency bazel_toolchains to v1 (#1214)
• Update dependency io_bazel_rules_go to v0.19.5 (#1213)
• Update rules_python commit hash to 5aa465d (#1211)
• Update io_bazel_rules_scala commit hash to b2273e7 (#1210)
• Update io_bazel_rules_rust commit hash to 29acd8f (#1209)
• making changes to simplify py toolchains (#1206)
• testing changes to platforms to enable #1203 to work (#1205)
• update container dependencies (#1202)
• Fix writing uncompressed images & add test (#1201)
• Support env vars that contain '=' (#1200)
• update go containerregistry for #1193 (#1197)
• Update README & bazelrc (#1195)