Publish javadoc / reference docs to spring.io

[pderop]

This PR is meant to publish javadoc and reference docs to docs.spring.io/projecrtreactor/reactor-netty/

In this PR, a new deployDocs gradle plugin is used to prepare/upload and install javadoc/reference docs.
The deployDocs gradle plugin is now using SimpleSSH java library which supports JDK 8, so it drastically simplifies everything.

note that SimpleSSH depends on an old com.jcraft:jsch project which is deprecated and this PR replaces it with https://github.com/mwiede/jsch, which can be used as a drop-in replacement for old com.jcraft:jsch.

on each push, the following docs will be updated here:

https://docs.spring.io/projectreactor/reactor-netty/docs/VERSION/api/ (javadoc)
https://docs.spring.io/projectreactor/reactor-netty/docs/VERSION/reference/html/ (reference doc)
https://docs.spring.io/projectreactor/reactor-netty/docs/VERSION/reference/pdf/ (pdf reference doc)
https://docs.spring.io/projectreactor/reactor-netty/docs/current -> (the latest stable docs)
https://docs.spring.io/projectreactor/reactor-netty/docs/current-SNAPSHOT -> (the most recent snapshot docs)
https://docs.spring.io/projectreactor/reactor-netty/docs/<major>.<minor>.x -> (the most recently released version starting with <major>.<minor>)
https://docs.spring.io/projectreactor/reactor-netty/docs/<major>.<minor>.x-SNAPSHOT -> (the most recent snapshot docs starting with <major>.<minor>)

you can check existing docs which have been manually uploaded in https://docs.spring.io/projectreactor/reactor-netty/docs/

[pderop]

actually, in previous closed #3345 PR, we were using the latest version of org.hidetake.ssh (2.11.2), and it was requiring JDK11.

Now, spring-security is using an older version of org.hidetake.ssh: 2.10.1, and this version is JDK8 compatible !
see https://github.com/spring-projects/spring-security/blob/main/gradle/libs.versions.toml#L102

So, last forced push is now using org.hidetake.ssh 2.10.1 (the exact same version used by spring-security).

[pderop]

thanks @violetagg for the review!

[pderop]

there is a remaining issue in the build of the merged PR: https://github.com/reactor/reactor-netty/actions/runs/9904990175/job/27363908378

I am checking it now.

[pderop]

This PR has been merged, but after, has been reverted, because it still does not work, see https://github.com/reactor/reactor-netty/actions/runs/9908800193/job/27375769400

> Task :reactor-netty:deployDocs
Retrying: com.jcraft.jsch.JSchException: reject HostKey: ***
Retrying: com.jcraft.jsch.JSchException: reject HostKey: ***
Retrying: com.jcraft.jsch.JSchException: reject HostKey: ***
Retrying: com.jcraft.jsch.JSchException: reject HostKey: ***
Retrying: com.jcraft.jsch.JSchException: reject HostKey: ***

FAILURE: Build failed with an exception.

* What went wrong:
Execution failed for task ':reactor-netty:deployDocs'.
> com.jcraft.jsch.JSchException: reject HostKey: ***

I suspect that it's because the org.hidetake.ssh' version '2.10.1' that is used by this PR has a transitive dependency to com.jcraft:jsch which is deprecated and has compatibiliy problems with latest openssh keys format.

see https://stackoverflow.com/questions/53134212/invalid-privatekey-when-using-jsch

on my own lab, I could reproduce and replacing the old com.jcraft jsch library by https://github.com/mwiede/jsch (drop in replacement) worked: to use it, the following can be done:

• get this PR + the additional commit from 16cdaaf
• add in buildSrc this build.gradle patch:

/*
 * Copyright (c) 2024 VMware, Inc. or its affiliates, All Rights Reserved.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *   https://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
plugins {
	id 'groovy'
}

repositories {
	gradlePluginPortal()
	mavenCentral()
}

dependencies {
	implementation localGroovy()
	implementation "com.github.mwiede:jsch:0.2.5"
	implementation("org.hidetake:gradle-ssh-plugin:2.10.1") {
		exclude group: 'com.jcraft', module: 'jsch'
	}
}

and remove the following from the toplevel build.gradle:

id 'org.hidetake.ssh' version '2.10.1' apply false

Now, I did not complete the PR with the above, because I cannot prove that com.github.mwiede:jsch:0.2.5 is also used by spring-security (spring-security is also using org.hidetake:gradle-ssh-plugin:2.10.1, but it seems to also use com.jcraft:jsch old artifact).

see https://github.com/spring-projects/spring-security/blob/main/buildSrc/src/main/groovy/io/spring/gradle/convention/DeployDocsPlugin.groovy and https://github.com/spring-projects/spring-security/blob/main/gradle/libs.versions.toml#L103

so, that's why for the moment, this PR has been reverted.

@violetagg , please update this PR with the proper labels in order to indicate that it has been reverted (I'm not sure).

thanks.