[jaxrs-spec] Add builders to models

[shybovycha]

As per #2415, adding builders generation for models.

The reasons for this change are:

1. currently the setters do not have the set prefix, which makes models not comply with java beans requirements
2. constructing models becomes painful, specifically when they have numerous fields

Compare the current way to construct a model to the proposed one:

now:

new Model().property1(value1).property2(value2)

// getters/setters

myModel.getProperty1();
myModel.property1(value1);

proposed:

Model.builder().property1(value1).property2(value2).build()

// getters/setters

myModel.getProperty1();
myModel.setProperty1(value1);

PR checklist

• Read the contribution guidelines.
• If contributing template-only or documentation-only changes which will change sample output, build the project before.
• Run the shell script(s) under ./bin/ (or Windows batch scripts under.\bin\windows) to update Petstore samples related to your fix. This is important, as CI jobs will verify all generator outputs of your HEAD commit, and these must match the expectations made by your contribution. You only need to run ./bin/{LANG}-petstore.sh, ./bin/openapi3/{LANG}-petstore.sh if updating the code or mustache templates for a language ({LANG}) (e.g. php, ruby, python, etc).
• File the PR against the correct branch: master, 4.3.x, 5.0.x. Default: master.
• Copy the technical committee to review the pull request if your PR is targeting a particular programming language.

[shybovycha]

JFYI: bitrise build is wrong - it tries to do something for swift4 with swift5-all.sh script, which apparently does not exist. Should the builds depend on the branch (e.g. swift4 for non-5.x branch and swift5 for 5.x)?

sh: bin/swift5-all.sh: No such file or directory
|                                                                              |
+---+---------------------------------------------------------------+----------+
| x | Update Swift4 samples (exit code: 127)                        | 33.32 sec|
+---+---------------------------------------------------------------+----------+
| Issue tracker: https://github.com/bitrise-io/steps-script/issues             |
| Source: https://github.com/bitrise-io/steps-script                           |
+---+---------------------------------------------------------------+----------+

[wing328]

The bitwise failure can be ignored as we just added the Swift 5 generator to the master.

[wing328]

I noticed that the body parameter name changes from user to body. Likely you're not using the latest (or recent) master when creating this PR.

Please merge the latest master of the official repo into your branch and regenerate the sample again.

[shybovycha]

I have used 4.3.x as the origin of my branch, are you sure I should merge master in?

[wing328]

OK. Please put it on hold. I'll take another look over the weekend or next week.

[wing328]

If this setting defaults to false, you can then target this change to the current master as it's no longer a breaking change. Otherwise, you will need to wait for 4.3.0 to be released on Feb 29.

[shybovycha]

To name the branch accordingly and restart the failing builds I'll close this PR and open a new one, with the correct target branch.