[CHE 6] Revert renaming of "Agents" by "Installers"

Description

For some reasons, “Agents” have been renamed to “Installers” in our model. This nomenclature is unfortunate and must be reverted.

The meaning behind “installers” is completely different from end-user point of view. An installer does not provide any features or capabilities - it is just a component that handle the installation of a “software”.

“Installer” is unfortunated because:

• On some infrastructures there is nothing which can be installed in a workspace machine(s)
• Agents might be packaged in the workspace machine(s)
• Agents can be running as sidecars of the workspace machine(s)

“Installers” nomenclature is more confusing than anything for end-users - and very specific to one scenario.

Example showing how it is exposed to end-user:

Here, the user is supposed to enable features and capabilities provided by “Agents” not “Installers”

That renaming also breaks any workspace definition (used in chefile, factories) between che5 and che6:

"dev-machine": {
  "installers": [
    "org.eclipse.che.exec",
    "org.eclipse.che.terminal",
    "org.eclipse.che.ws-agent",
    "org.eclipse.che.ssh"
  ],
}

Here it looks equally unappropriated.

[ghost]

The purpose of an installer is quite straightforward. An installer installs software and services, start servers, activates agents etc. Some of the servers are crucial to the IDE and workspace in general, such as workspace agent, exec agent and terminal. Others just bring new functionality to a workspace - language servers, SSH daemon. Bootstrapper executes installer scripts that prepare environment, check for dependencies and install components defined by an installer. You may want to take a look at an example of an installer script that prepares environment and installs C# language server.

This is what I have in Che6 docs as a draft. And this is exactly what an installer script does.

[gazarenkov]

@gorkem but that’s exactly how it works now, we point to the script which installs software on running machine (container or PC, whatever), it is not a “right cloud solution”. If you think “installer” is the bad word then propose other but if it is “agent” then propose other word for what we call “agent” now (the soft we actually install).

@slemeur
we are trying to convince you that "installer" is not an appropriated wording to name a tool to prepare environment, deliver and launch agents as in many cases, nothing will be "installed". No needs to convince me, I agree that in case we do not need “installer” we do not include it in workspace definition (add something else instead).

The way the agents are delivered to the end-user is the problem of our infrastructure. that was the problem of Che5 since in this case user who wanted just to add a script to install software had to be aware of infrastructure specific mechanism to to deliver and run this script. In Che6 it is improved adding one more layer called “bootstrapper” as an infrastructure specific mechanism of delivery installers to this particular infrastructure. So it lowers threshold for installer (just a script) author and makes installer launch-able on potentially any infrastructure which supports it (i.e. has “bootstrapper”).