MINOR: Various README tweaks

[ijuma]

1. Fix ambiguous statement where it could be interpreted that scalac is used for the clients module
2. Remove "in KRaft mode" because that's the only mode
3. Put IntelliJ first in IDE section and only mention the native gradle integration
4. Restore instructions for installing all projects to the local Maven repo, this was accidentally removed as part of the Scala 2.12 support removal.

Committer Checklist (excluded from commit message)

• Verify design and implementation
• Verify test coverage and CI build status
• Verify documentation (including upgrade notes)

[chia7712]

@ijuma thanks for this patch. There are two trivial comments remaining.

[chia7712]

maybe we can remove idea plugin from build.gradle?

https://github.com/apache/kafka/blob/trunk/build.gradle#L35

[ijuma]

This is a larger change as it would break someone who is using this plugin in their workflow (for whatever reason). I'd prefer to start by removing it from the README (to keep things simple for new contributors) and leaving the actual plugin removal for later. Is that reasonable?

[chia7712]

Could we combine this with line #178 into a single command? Maybe ./gradlew -PskipSigning=true publishToMavenLocal is good enough

[ijuma]

Good point. I'll still keep the separate line for the single project case, but will add the -PskipSigning=true to this one.

[ijuma]

Pushed this change.

[mumrah]

@ijuma #17881 adds a "triage" label to PRs from non-committers. Turns out this also affect committers if their membership visibility in the ASF GitHub org is not public. I added instructions for setting your membership visibility to public https://github.com/apache/kafka/blob/trunk/.github/workflows/README.md#pr-triage

The label was removed from this PR since it was reviewed, but if you want to avoid it being added to your future PRs see the link above

[ijuma]

@mumrah Thanks for the heads up, I have changed the visibility to public as documented.