[JENKINS-66253] - Update the minimum Jenkins version from 2.235.1 to 2.263.1

[Onyimatics]

• Make sure you are opening from a topic/feature/bugfix branch (right side) and not your main branch!
• Ensure that the pull request title represents the desired changelog entry
• Please describe what you did
• Update the minimum Jenkins version from 2.235.1 to 2.263.1.
• Link to relevant issues in GitHub or Jira
• JENKINS-66253

@MarkEWaite @oleg-nenashev

[MarkEWaite]

Based on plugin installation statistics, the publish-over-ssh plugin installations form two major groups:

1. 1.20.1 (released in 2018) with over 90% of 1.20.1 users running Jenkins core before 2.263.1
2. 1.22 (released in 2021) with over 90% of 1.22 users running Jenkins core 2.263.1 or later

The item 1 users are not upgrading Jenkins core or the plugin, so are unlikely to take a new release. The item 2 users are already running 2.263.1 or later so are not harmed by the plugin requiring 2.263.1 as its minimum Jenkins version.

Installation count combining item 1 (release 1.20.1) and item 2 (release 1.22) accounts for 89% of the total plugin installations.

Thanks for the pull request!