feat(docs): add ADR for DI

[InAnYan]

Closes https://github.com/JabRef/jabref-issue-melting-pot/issues/590

Just added an ADR.

Steps to test

No steps to test. Just check the contents.

Mandatory checks

• [x] I own the copyright of the code submitted and I license it under the MIT license
• [x] I manually tested my changes in running JabRef (always required)
• [/] I added JUnit tests for changes (if applicable)
• [/] I added screenshots in the PR description (if change is visible to the user)
• [/] I described the change in CHANGELOG.md in a way that is understandable for the average user (if change is visible to the user)
• [x] I checked the user documentation: Is the information available and up to date? If not, I created an issue at https://github.com/JabRef/user-documentation/issues or, even better, I submitted a pull request updating file(s) in https://github.com/JabRef/user-documentation/tree/main/en.

[jabref-machine]

You modified Markdown (*.md) files and did not meet JabRef's rules for consistently formatted Markdown files. To ensure consistent styling, we have markdown-lint in place. Markdown lint's rules help to keep our Markdown files consistent within this repository and consistent with the Markdown files outside here.

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[InAnYan]

• [ ] TODO: We use @Inject only in Views, not in ViewModels. And this again helps in testing, as ViewModel uses constructor-based DI

[koppor]

• [ ] TODO @Inject for JAX-RS services - there, we use jakarta.inject.Inject and hk2: org.glassfish.hk2.api.ServiceLocator

[calixtus]

https://github.com/dlsc-software-consulting-gmbh/FxmlKit