chore: keep only one Dockerfile per Linux image variant

[lemeurherve]

This PR simplifies this repo content by keeping only one Dockerfile per Linux image variant like the Windows images, versus one per JDK and per Linux image variant currently.

Notes:

• Use the JDK17 image (current default Jenkins JDK version) from each variant as their new unique Dockerfile base
  • Moving commit: https://github.com/jenkinsci/docker/pull/1857/commits/214019e9a268bdacb8cf4a87eaee70c04895a1de
  • Cleanup commit: https://github.com/jenkinsci/docker/pull/1857/commits/c33b4affdb9f2229496af80563a184bf54f441cf
  • Little exception for Almalinux & RHEL ubi8: they only have one JDK11 version, used as bases.
• Factorize jlink command depending on the JDK version and adapt docker bake paths:
  • Distinct commit: https://github.com/jenkinsci/docker/pull/1857/commits/a181b22b9f5a2a62b05aee55d1d3e81496e0abe9
  • This jlink code block is based on a proven implementation coming from the agent images: https://github.com/jenkinsci/docker-agent/blob/e2560a929884a1f1cfe3c64001b1b2932d8e7057/debian/Dockerfile#L32-L51
  • I've adapted it to be POSIX compliant as the Alpine ash shell doesn't support arrays: https://github.com/jenkinsci/docker/pull/1857/files#diff-e65ec3bff5dbf5186d16b4f5630439bbe16f82258447f5f212ad42e4ac897e60R28-R33
  • Side note: this should probably be replicated in the Alpine agent image, which doesn't currently specify any shell
  • ~I'm also passing a new JLINK_COMPRESS argument depending on the JDK version as a Dockerfile ARG~
  • ~I find it cleaner than adding conditions in the RUN if case else block, which would also be challenging in the Alpine variant due to the lack of arrays support by ash.~
  • Reworked in https://github.com/jenkinsci/docker/pull/1857/commits/b8ff4f7dba5426c166968e266d04c14691b7cfc7 and https://github.com/jenkinsci/docker/pull/1857/commits/e672c5ceaadaf7538292421597b4ad95816227b5 to take in account the following review: https://github.com/jenkinsci/docker/pull/1857#pullrequestreview-2019551477
    • This wasn't that challenging actually
    • I took the opportunity to keep only the POSIX shell compliant version everywhere using set instead of arrays
  • Again, little exception for Almalinux & RHEL ubi8: as they only have one JDK11 version, their Dockerfiles remain untouched.
• I've done a last little bit of quoting to satisfy shellcheck: https://github.com/jenkinsci/docker/pull/1857/commits/1e0037bdfbe8c4d1a4b9ed5cc7ff74543e6b2486

For the record, initial image content changes extracted to other merged pull requests:

> - Non integration of the `install-plugins.sh` shell script in JDK11 images: > - Deprecated since September 2020 > - Does only echo a warning since https://github.com/jenkinsci/docker/pull/1408 almost two years ago: https://github.com/jenkinsci/docker/blob/bed10d624086e931cf1d053d62174a2355cfd15c/install-plugins.sh > - I think it's time for it to go, it shouldn't functionally change anything for the end users anyway. > - Extracted to https://github.com/jenkinsci/docker/pull/1863 if it needs to be merged separately. > - JDK21 specific compression argument set to `zip-6` like Linux for Windows image: > - https://github.com/jenkinsci/docker/pull/1857/commits/7d1817117127c9d6461d8e2c9fc63fd8466d8c2e > - Complement of https://github.com/jenkinsci/docker/pull/1848 which introduced jlink in the Windows controller image > - Note: jlink on Windows should be properly tested, might worth its own issue > - Extracted to https://github.com/jenkinsci/docker/pull/1864 if it needs to be merged separately.

I'll create a follow-up pull request to adapt updatecli manifests to these changes. (Preview: https://github.com/jenkinsci/docker/commit/65353f93adb51fa12dedfd95c0bb34d3b06ab357)

This PR is a first step, I'd like to factorize a bit the logic of the docker bake around jdk versions after that.

Testing done

Local builds + CI

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[lemeurherve]

Addressed spread in https://github.com/jenkinsci/docker/pull/1857/commits/b8ff4f7dba5426c166968e266d04c14691b7cfc7 and https://github.com/jenkinsci/docker/pull/1857/commits/e672c5ceaadaf7538292421597b4ad95816227b5 with minimal complexity.

Not sure putting this into a separate script is mandatory for this PR.

[olivergondza]

On behalf of rhel images, I can say I do not object, as the matrix of versions and jdks remain unchanged. Added one question/suggestion.

[lemeurherve]

Opened #1857 & #1864 if the minor image changes of this PR need to be merged separately.

EDIT: merged.