Add soundness workflows (apple#701)

Adds CI for the following checks:
- YAML lint
- Python lint
- Unacceptable language
- Broken symlinks
- API breakages

In the future the following checks will be added:
- Documentation
- License headers
- Formatting
- Shell check

Author: rauhul

.editorconfig

@@ -0,0 +1,7 @@
+root = true
+
+[*]
+indent_style = space
+indent_size = 2
+trim_trailing_whitespace = true
+insert_final_newline = true

.github/workflows/lint.yml

@@ -0,0 +1,16 @@
+name: Pull request
+
+on:
+  pull_request:
+    types: [opened, reopened, synchronize]
+
+jobs:
+  soundness:
+    name: Soundness
+    uses: swiftlang/github-workflows/.github/workflows/soundness.yml@main
+    with:
+      docs_check_enabled: false  # bug: https://github.com/apple/swift-argument-parser/issues/704
+      format_check_enabled: false  # bug: https://github.com/apple/swift-argument-parser/issues/702
+      license_header_check_enabled: false  # feature: https://github.com/swiftlang/github-workflows/issues/78
+      license_header_check_project_name: "Swift Argument Parser"  # bug: https://github.com/swiftlang/github-workflows/issues/76
+      shell_check_enabled: false  # bug: https://github.com/apple/swift-argument-parser/issues/703

.spi.yml

@@ -2,4 +2,3 @@ version: 1
 builder:
   configs:
     - documentation_targets: [ArgumentParser]
-

.unacceptablelanguageignore

@@ -0,0 +1,2 @@
+# Ignore this file which references the "master" branch of another repo
+Tools/generate-manual/MDoc/MDocMacro.swift