(gh-35) Make install.json optional parameters consistent

Strictly speaking, given that the parameters have defaults, it should
not be necessary to type them 'Optional' in install.json.

But the install task is used as the puppet_library plugin for installing
openvox via apply_prep, and something about how Bolt constructs the task
there causes a failure for non optional parameters, even if they have
defaults:

  jpartlow@archimedes:~/work/src/kvm_automation_tooling$ cat plans/test.pp
  plan kvm_automation_tooling::test() {
    apply_prep('b-alma9-ov8-agent-1')
  }
  jpartlow@archimedes:~/work/src/kvm_automation_tooling$ be bolt plan run kvm_automation_tooling::test --inventory terraform/instances/inventory.b-alma9-ov8.yaml
  Starting: plan kvm_automation_tooling::test
  Starting: install puppet and gather facts on b-alma9-ov8-agent-1
  Finished: plan kvm_automation_tooling::test in 0.27 sec
  Failed on b-alma9-ov8-agent-1:
    Error executing plugin task from puppet_library: Task openvox_bootstrap::install:
     expects a value for parameter 'package'
  Failed on 1 target: b-alma9-ov8-agent-1
  Ran on 1 target

Some parameters will be wired into openbolt's DEFAULT_PLUGIN_HOOKS
(https://github.com/OpenVoxProject/openbolt/blob/b9bff5a8dfe2f41218281bf8c5e6ad901bcae460/lib/bolt/plugin.rb#L133)
and stop_service is already one of them, but to keep everything
consistent, I'm setting all the parameters optional with the defaults
explicit so that it's at least clear to a caller running
'bolt task show openvox_bootstrap::install' what must be provided and
what the defaults are.

Author: jpartlow

tasks/install.json

@@ -3,12 +3,13 @@
   "parameters": {
     "package": {
       "description": "The name of the package to install.",
-      "type": "String[1]",
+      "type": "Optional[String]",
       "default": "openvox-agent"
     },
     "version": {
-      "description": "The version of the openvox-agent package to install. Defaults to latest.",
-      "type": "Optional[String]"
+      "description": "The version of the openvox-agent package to install.",
+      "type": "Optional[String]",
+      "default": "latest"
     },
     "collection": {
       "description": "The openvox collection to install from.",