Add script to make testing of code on branches easier (#1844)

## Changes

Convenience script to exec into a shell where a CLI build for a specific
branch is made available.

## Tests

Manually from `/tmp` with `bash <([path]) demo-dashboards`.

internal/bugbash/README.md

@@ -0,0 +1,13 @@
+# Bugbash
+
+The script in this directory can be used to conveniently exec into a shell
+where a CLI build for a specific branch is made available.
+
+## Usage
+
+This script prompts if you do NOT have at least Bash 5 installed,
+but works without command completion with earlier versions.
+
+```shell
+bash <(curl -fsSL https://raw.githubusercontent.com/databricks/cli/main/internal/bugbash/exec.sh) my-branch
+```

internal/bugbash/exec.sh

@@ -0,0 +1,139 @@
+#!/usr/bin/env bash
+
+set -euo pipefail
+
+# Set the GitHub repository for the Databricks CLI.
+export GH_REPO="databricks/cli"
+
+# Synthesize the directory name for the snapshot build.
+function cli_snapshot_directory() {
+    dir="cli"
+
+    # Append OS
+    case "$(uname -s)" in
+    Linux)
+        dir="${dir}_linux"
+        ;;
+    Darwin)
+        dir="${dir}_darwin"
+        ;;
+    *)
+        echo "Unknown operating system: $os"
+        ;;
+    esac
+
+    # Append architecture
+    case "$(uname -m)" in
+    x86_64)
+        dir="${dir}_amd64_v1"
+        ;;
+    i386|i686)
+        dir="${dir}_386"
+        ;;
+    arm64|aarch64)
+        dir="${dir}_arm64"
+        ;;
+    armv7l|armv8l)
+        dir="${dir}_arm_6"
+        ;;
+    *)
+        echo "Unknown architecture: $arch"
+        ;;
+    esac
+
+    echo $dir
+}
+
+BRANCH=$1
+shift
+
+# Default to main branch if branch is not specified.
+if [ -z "$BRANCH" ]; then
+  BRANCH=main
+fi
+
+if [ -z "$BRANCH" ]; then
+  echo "Please specify which branch to bugbash..."
+  exit 1
+fi
+
+# Check if the "gh" command is available.
+if ! command -v gh &> /dev/null; then
+  echo "The GitHub CLI (gh) is required to download the snapshot build."
+  echo "Install and configure it with:"
+  echo ""
+  echo "  brew install gh"
+  echo "  gh auth login"
+  echo ""
+  exit 1
+fi
+
+echo "Looking for a snapshot build of the Databricks CLI on branch $BRANCH..."
+
+# Find last successful build on $BRANCH.
+last_successful_run_id=$(
+  gh run list -b "$BRANCH" -w release-snapshot --json 'databaseId,conclusion' |
+      jq 'limit(1; .[] | select(.conclusion == "success")) | .databaseId'
+)
+if [ -z "$last_successful_run_id" ]; then
+  echo "Unable to find last successful build of the release-snapshot workflow for branch $BRANCH."
+  exit 1
+fi
+
+# Determine artifact name with the right binaries for this runner.
+case "$(uname -s)" in
+Linux)
+    artifact="cli_linux_snapshot"
+    ;;
+Darwin)
+    artifact="cli_darwin_snapshot"
+    ;;
+esac
+
+# Create a temporary directory to download the artifact.
+dir=$(mktemp -d)
+
+# Download the artifact.
+echo "Downloading the snapshot build..."
+gh run download "$last_successful_run_id" -n "$artifact" -D "$dir/.bin"
+dir="$dir/.bin/$(cli_snapshot_directory)"
+if [ ! -d "$dir" ]; then
+    echo "Directory does not exist: $dir"
+    exit 1
+fi
+
+# Make CLI available on $PATH.
+chmod +x "$dir/databricks"
+export PATH="$dir:$PATH"
+
+# Set the prompt to indicate the bugbash environment and exec.
+export PS1="(bugbash $BRANCH) \[\033[01;32m\]\u@\h\[\033[00m\]:\[\033[01;34m\]\w\[\033[00m\]\$ "
+
+# Display completion instructions.
+echo ""
+echo "=================================================================="
+
+if [[ ${BASH_VERSINFO[0]} -lt 5 ]]; then
+    echo -en "\033[31m"
+    echo "You have Bash version < 5 installed... completion won't work."
+    echo -en "\033[0m"
+    echo ""
+    echo "Install it with:"
+    echo ""
+    echo "  brew install bash bash-completion"
+    echo ""
+    echo "=================================================================="
+fi
+
+echo ""
+echo "To load completions in your current shell session:"
+echo ""
+echo "  source /opt/homebrew/etc/profile.d/bash_completion.sh"
+echo "  source <(databricks completion bash)"
+echo ""
+echo "=================================================================="
+echo ""
+
+# Exec into a new shell.
+# Note: don't use zsh because on macOS it _always_ overwrites PS1.
+exec /usr/bin/env bash