0.2.13 changes

[norrisjeremy]

• Upload large file getting stuck #411 add flush operation from Fix added is/jsch#39, with new config option to allow disabling in case it causes regressions.
• Update dependencies.
• Add Java 21 to CI pipeline and also use it by default for building.
• Switch CI pipelines to using maven wrapper and produce any execution error messages.
• channel.getInputStream() should warn if the channel has already connected #403 add a warning when Channel.getInputStream() or Channel.getExtInputStream() is called after Channel.connect().

[norrisjeremy]

FYI, may need to adjust checks for PRs to also mark the Java 21 builds as required after merging this.