fix(gatsby): don't print out flag suggestions if none are enabled or opted-in

[pieh]

Description

gatsby develop due to some LOCKED_IN flag was always priting other flag suggestions even tho there was no explicit flags enabled by users or flags auto opted-in (both of which would print some message). It was resulting in confusing output like:

$ gatsby develop
info

There are 6 other flags available that you might be interested in:
- FAST_DEV · Enable all experiments aimed at improving develop server start time
- DEV_SSR · (Umbrella Issue (https://gatsby.dev/dev-ssr-feedback)) · Server Side Render (SSR) pages on full reloads during develop. Helps you detect SSR bugs
and fix them without needing to do full builds.
- PRESERVE_WEBPACK_CACHE · (Umbrella Issue (https://gatsby.dev/cache-clearing-feedback)) · Use webpack's persistent caching and don't delete webpack's cache
when changing gatsby-node.js & gatsby-config.js files.
- PRESERVE_FILE_DOWNLOAD_CACHE · (Umbrella Issue (https://gatsby.dev/cache-clearing-feedback)) · Don't delete the downloaded files cache when changing
gatsby-node.js & gatsby-config.js files.
- PARALLEL_SOURCING · EXPERIMENTAL · (Umbrella Issue (https://gatsby.dev/parallel-sourcing-feedback)) · Run all source plugins at the same time instead of
serially. For sites with multiple source plugins, this can speedup sourcing and transforming considerably.
- FUNCTIONS · EXPERIMENTAL · (Umbrella Issue (https://gatsby.dev/functions-feedback)) · Compile Serverless functions in your Gatsby project and write them to
disk, ready to deploy to Gatsby Cloud

success open and validate gatsby-configs - 0.110s

This PR checks wether there is any message related to flags before trying to even suggest other flags

Related Issues

Fixes regression introduced in #30992

[LekoArts]

👍