feat: Add default, exec-based, startup probe to the deployment template

[ppawlowski]

Description

This pull request adds default startupProbe values for the Node-RED container.
In the presented approach, the startup probe invokes the curl command inside the container to query the /flowforge/ready endpoint on the management port and accepts both 200 and 404 HTTP statuses.
This approach allows enabling such configuration on the project containers created with nr-launcher version 2.23.1 and earlier.
Additionally, default startup probe:

• waits 5 seconds after container startup
• executes every 2 seconds
• expects 1 successful response
• accepts 450 consecutive failures before restarting the pod

Related Issue(s)

#233

Checklist

• I have read the contribution guidelines
• Suitable unit/system level tests have been added and they pass
• Documentation has been updated
  • Upgrade instructions
  • Configuration details
  • Concepts
• Changes flowforge.yml?
  • Issue/PR raised on FlowFuse/helm to update ConfigMap Template
  • Issue/PR raised on FlowFuse/CloudProject to update values for Staging/Production
• Link to Changelog Entry PR, or note why one is not needed.

Labels

• Includes a DB migration? -> add the area:migration label