chore: Refactor docker-compose to simplify installation experience

[ppawlowski]

Description

This pull request refactors the 'main' docker compose file used for FlowFuse installation on self-hosted environments. Additionally, it introduces:

• .env.example file for persistent configuration
• docker-compose-tls.override.yml file for TLS management

Included changes should be merged together with FlowFuse/flowfuse#4665

Related Issue(s)

FlowFuse/flowfuse#4633

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

Labels

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

[hardillb]

The upgrade instructions are going to be interesting with the changes to named volumes over local directories.

How will an exisiting user upgrade and keep using the local directories or copy them to the named volumes?

[ppawlowski]

The upgrade instructions are going to be interesting with the changes to named volumes over local directories.

How will an exisiting user upgrade and keep using the local directories or copy them to the named volumes?

I added upgrade instructions which I tested beforehand. Feel free to verify them on your end as well.

[hardillb]

Looks good.

Only question, where is TLS_ENABLED set? I only see it mentioned in the docker-compose.yml but not anywhere else

[ppawlowski]

Only question, where is TLS_ENABLED set? I only see it mentioned in the docker-compose.yml but not anywhere else

Added to .env.example to avoid confusion.

[ppawlowski]

@hardillb I've extended compose file and added the possibility to configure smtp settings. Please review one more time.