Simplify enabling of connectors within modeler

[nikku]

What should we do?

Related to #4302 we want to ensure that it is simple to enable connectors within the app, i.e. on first time startup. This allows users to get a better out-of-the-box experience for Camunda + connectors.

• We explore introducing a minimal settings page to accomplish this, hence it is related to Be able to configure preferences / settings / flags via UI #2913
  • Not part of first iteration
• We want to load/update connector templates lazily, only when a user opens a Camunda 8 diagram (Enable connector templates per default #4474)
• We want connectors to be enabled automatically, and indicate ability to configure via the what's new communication (Enable connector templates per default #4474)
• Rename flag to disable-connector-templates (chore: rename flag to disable-connector-templates #4479)
• We want to update documentation accordingly (Update Desktop Modeler connector template documentation camunda-docs#4187)

Why should we do it?

Ensure users have a simpler out-of-the-box experience for Camunda + connectors.

[crobbins215]

Discussed on slack, adding info to the ticket.

Let's enable it by default but with a settings page so it can be disabled if required.

[nikku]

Decided in the kick-off:

• We want to load/update connector templates lazily, only when a user opens a Camunda 8 diagram
• We want connectors to be enabled automatically, and indicate ability to disable them via the what's new communication
• We want to update documentation accordingly

[nikku]

Work in progress PR (iteration 1, missing tests and updated what's new communication) is available via #4474.

[nikku]

Typical time it takes to update connectors is around 40 (!) seconds:

Unfortunately the marketplace API we use for testing does not provide us with the information needed for more finegrained fetching.