clarify spring boot conventions for config, update spring links

[conceptualshark]

Description

Resolves #3501

• Added an explicit callout and links to the Spring docs on external configs to spring components
• Updated existing spring doc links
• Where we specifically call out using a config file, added examples of converting the property name to an env variable (did not add this to pages where we only discuss env variables to begin with)

When should this change go live?

• This is a bug fix, security concern, or something that needs urgent release support.
• This is already available but undocumented and should be released within a week.
• This on a specific schedule and the assignee will coordinate a release with the DevEx team. (apply hold label or convert to draft PR)
• This is part of a scheduled alpha or minor. (apply alpha or minor label)
• There is no urgency with this change and can be released at any time.

PR Checklist

• My changes are for an already released minor and are in /versioned_docs directory.
• My changes are for the next minor and are in /docs directory (aka /next/).

• My changes require an Engineering review, and I've assigned the Engineering DRI or delegate.
• My changes require a technical writer review, and I've assigned @camunda/tech-writers as a reviewer.

[aabouzaid]

I'm not sure about this. I remember that Console doesn't support the Spring convention out of the box, only what we agreed on.

[aabouzaid]

Great work 🙌

Apart from the Console part which we need to review with the Console team, I'd approve this reset of the changes.