Generate cache key based on Job invocation

Attempt to capture as much context as possible about the job run
to generate a unique cache key. Unfortunately much of the matrix context
is not available to the action implementation.

__tests__/cache-utils.test.ts

@@ -2,30 +2,14 @@ import * as cacheUtils from '../src/cache-utils'
 import * as path from 'path'
 
 describe('cacheUtils-utils', () => {
-    describe('can truncate args', () => {
-        test('handles zero-length string', () => {
-            expect(cacheUtils.truncateArgs('')).toBe('')
+    describe('can hash', () => {
+        it('a string', async () => {
+            const hash = cacheUtils.hashStrings(['foo'])
+            expect(hash).toBe('acbd18db4cc2f85cedef654fccc4a4d8')
         })
-        test('leaves short string untouched', () => {
-            expect(
-                cacheUtils.truncateArgs('short string that-should-be-untouched')
-            ).toBe('short string that-should-be-untouched')
-        })
-        test('truncates long string', () => {
-            const longString = 'a'.repeat(500)
-            expect(cacheUtils.truncateArgs(longString)).toBe('a'.repeat(400))
-        })
-        test('trims leading and trailing whitespace', () => {
-            expect(cacheUtils.truncateArgs('    this is an arg      ')).toBe(
-                'this is an arg'
-            )
-        })
-        test('removes repeated whitespace', () => {
-            expect(
-                cacheUtils.truncateArgs(
-                    '   this     one     has long   \t\n\t\r  spaces    '
-                )
-            ).toBe('this one has long spaces')
+        it('multiple strings', async () => {
+            const hash = cacheUtils.hashStrings(['foo', 'bar', 'baz'])
+            expect(hash).toBe('6df23dc03f9b54cc38a0fc1483df6e21')
         })
     })
 })