Install plugins in existing session

[mofojed]

As a user of Deephaven, I want to be able to easily install plugins without having to configure Dockerfiles, or even restart my session.

E.g. If we could pip install the plugin within an existing session by running something like:

import os

os.system("pip install deephaven-plugin-matplotlib")

import deephaven.plugin.matplotlib
deephaven.plugin.matplotlib.register()

Or:

import os

os.system("pip install deephaven-plugin-matplotlib")

import deephaven.plugin
deephaven.plugin.auto_register_new()

It would make plugins much easier to install/use. Currently it requires pulling separate docker containers or modifying docker compose files, which is a bit of a pain.

Would also like to be able to install JS plugins similarly (though obviously wouldn't work via a pip install).

[devinrsmith]

The relevant place to look at the current logic on startup is io.deephaven.server.plugin.PluginRegistration#registerAll. If we want this to be more dynamic, we essentially need to keep a ref to io.deephaven.server.plugin.PluginRegistrationVisitor and plumb dynamic registrations through that object.

If we want an auto-discovery method, it may be useful to consider adding this to ObjectService more generally:

service ObjectService {
    ...
    rpc AutoRegisterNew(AutoRegisterNewRequest) returns (AutoRegisterNewResponse) {}
}