feat(eslint-plugin): add schematic support for flat configs

[timdeschryver]

PR Checklist

Please check if your PR fulfills the following requirements:

• The commit message follows our guidelines: https://github.com/ngrx/platform/blob/main/CONTRIBUTING.md#commit
• Tests for the changes have been added (for bug fixes / features)
• Documentation has been added / updated (for bug fixes / features)

PR Type

What kind of change does this PR introduce?

[ ] Bugfix
[x] Feature
[ ] Code style update (formatting, local variables)
[ ] Refactoring (no functional changes, no api changes)
[ ] Build related changes
[ ] CI related changes
[ ] Documentation content changes
[ ] Other... Please describe:

What is the current behavior?

The current schematic only supports the "old" ESLint configuration, which exists in a JSON file.

Closes #4643

What is the new behavior?

This PR adds support to add the NgRx plugin to the flat config (Eslint v9.
It supports the following formats:

• eslint.config.js
• eslint.config.mjs
• eslint.config.cjs

Does this PR introduce a breaking change?

[ ] Yes
[x] No

Other information

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[Copilot]

Copilot reviewed 2 out of 2 changed files in this pull request and generated 2 comments.

Comments suppressed due to low confidence (1)

modules/eslint-plugin/schematics/ng-add/index.ts:96

• If no import declarations exist, the insertion point defaults to 0, which may insert the new import statement in an unexpected location; consider handling this case separately to ensure the import is placed in a logical location relative to the tseslint.config call.

recorder.insertRight(lastImport?.end ?? 0, `\nimport ngrx from '${ngrxPlugin}';`);

[rainerhahnekamp]

Ouch - migrating to flat config isn’t as straightforward as it looks.
We went through something similar in Sheriff, and it definitely took some effort.
Fingers crossed the flat config stays stable for a few years now! 🤞