Add command "nomad tls"

[lhaig]

This PR adds the same functionality that is currently available in Consul.

It adds the following commands 'nomad tls ca create ' 'nomad tls cert create -server / -client / - cli ' 'nomad tls cert -info '

It also adds the docs

[lhaig]

• The create commands take an optional argument which determines the output file prefix. Is there a reason why this couldn't be a flag instead, which seems to suit the optional nature better?

I have removed this as the prefix did nothing in the code.

[lhaig]

• A couple of tests rely on t.Fatal and it would be nice if we could use require instead.

I have changed the test @jrasell but now I am thinking I should change the name of the test from TestValidateTLSCACreateCommand_noTabs to TestValidateTLSCACreateCommand_hasTabs

This is the new test

func TestValidateTLSCACreateCommand_HasTabs(t *testing.T) {
	t.Parallel()
	ui := cli.NewMockUi()
	cmd := &TLSCACreateCommand{Meta: Meta{Ui: ui}}
	code := cmd.Help()
	require.False(t, strings.ContainsRune(code, '\t'))
}

[tgross]

Preview link https://nomad-nttruonxz-hashicorp.vercel.app/nomad/docs/commands/tls

[tgross]

Let's get this merged so it can go out in the next release of Nomad (likely 1.4.4).

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