add install action to install all trunk tools in trunk.yaml (#234)

install will pull trunk launcher from cloud into tmp location and then
run the `trunk tools install` command.

Optionally installs that are specified - else installs everything.

Example of using it in flaky factory


https://github.com/trunk-io/flake-factory/blob/main/.github/workflows/factory.yaml

      - name: trunk install
uses:
54ccfcf

install/action.yaml

@@ -0,0 +1,35 @@
+name: Trunk Check
+author: trunk.io
+description: Install trunk and managed tools to PATH
+
+inputs:
+  tools:
+    description: specific tools to install (if not specified will install all enabled tools)
+    required: false
+
+branding:
+  icon: check
+  color: green
+
+runs:
+  using: composite
+  steps:
+    - name: get trunk
+      shell: bash
+      run: ${GITHUB_ACTION_PATH}/get_trunk.sh
+
+    - name: clean up possible dead symlink
+      shell: bash
+      run: |
+        tools_path=".trunk/tools"
+        if [ -L "${tools_path}" ] && [ ! -e "${tools_path}" ] ; then
+          rm "${tools_path}"
+        fi
+
+    - name: Trunk install
+      shell: bash
+      run: trunk tools install --ci ${{ inputs.tools }}
+
+    - name: Add .trunk/tools to path
+      shell: bash
+      run: echo ".trunk/tools" >> $GITHUB_PATH

install/get_trunk.sh

@@ -0,0 +1,20 @@
+#!/bin/bash
+
+set -euo pipefail
+
+if [[ ${INPUT_DEBUG:-false} == "true" ]]; then
+  set -x
+fi
+
+tmpdir="$(mktemp -d)"
+echo "TRUNK_TMPDIR=${tmpdir}" >>"${GITHUB_ENV}"
+
+curl -fsSL https://trunk.io/releases/trunk -o "${tmpdir}/trunk"
+chmod u+x "${tmpdir}/trunk"
+trunk_path="${tmpdir}/trunk"
+
+echo "TRUNK_PATH=${trunk_path}" >>"${GITHUB_ENV}"
+echo "${tmpdir}" >>"${GITHUB_PATH}"
+
+# Ensure that trunk CLI is downloaded before subsequent steps (swallow output of version command)
+(${trunk_path} version >/dev/null 2>&1) || echo "::warning::${trunk_path} does not exist!"