[Fleet] Create input package policy template assets when upgrading from type "integration" to "input"

[hop-dev]

Part of #133296

It is currently possible to change a package from type "integration" to type "input", package policy variables are mapped across.

Now that #145529 is complete, we create index and component templates for input packages at package policy creation time. Should we create these assets on package upgrade as well?

Considerations:

1. What if the data stream already exists and is managed by a different package?

   • Currently, when creating a package policy, if a user elects to send data to an existing data stream then the API force flag must be used. On upgrade we should inform the user that the data stream exists and is not managed by the package, and allow them to proceed.

2. Race conditions updating installed_es on installation SO

   • if a package has a lot of package policies e.g 1000 , and the user opts to automatically upgrade package policies, we would need to install 1000 lots of templates, the current code has basic concurrency control but is not designed for this level of concurrent work, we would have to do this installation in one go and updated installed_es once per package upgrade not once per package policy upgrade.

[elasticmachine]

Pinging @elastic/fleet (Team:Fleet)

[joshdover]

Should we create these assets on package upgrade as well?

If we don't create them during upgrade, do we at least create them the next time the user goes to edit the policy? If we have that workaround, I'd see this as more optional, but I agree it's a painpoint we'd probably want to fix sooner than later.