Cannot load a single value secret with loadSecret

[cajubelt]

Currently it is expected that secrets will be of the format

FOO=bar

But if they are just

my_secret

then they fail to parse. This should at least be documented, and ideally fixed.

Put another way, this test fails:

  it('still works if secret is single value', async () => {
    const fakeClient = {
      accessSecretVersion: async () => {
        return [{
          payload: {
            data: 'single_value_secret'
          }
        }]
      }
    } as unknown as SecretManagerServiceClient
    await expect(await loadSecret('/foo', fakeClient)).toBe('single_value_secret')
  })

AC:

• in-code docs updated to describe behavior parsing single-value secrets
• (optionally) test from description passes