Without this package, after Puppet has upgraded Jenkins and its plugins,
I see:

  Error: /Stage[main]/Jenkins::Cli/Exec[jenkins-cli]: Failed to call refresh: Could not find command 'jar'
  Error: /Stage[main]/Jenkins::Cli/Exec[jenkins-cli]: Could not find command 'jar'

The workaround introduced in 6b292cc0
for putting the website in maintenance reports "Under maintenance" for
any 503 and misleads people when the 503 is actually caused by some
other reason.

This commit reverts that behavior.

This reverts commit 4353d8bf.

See: https://salsa.debian.org/tails-team/gitlab-migration/-/issues/58

https://salsa.debian.org/tails-team/gitlab-migration/-/issues/48

Neither Weblate nor Django have built-in support for putting the website
in maintenance mode, so I'm adding the possibility of returning a 503
HTTP status code by touching a ".maintenance" file in Weblate's document
root.

Stored XSS vulnerability for Git plugin 3.12.1:

    https://jenkins.io/security/advisory/2020-03-09/#SECURITY-1723

The update of Mailer plugin was not mandatory but can save a bit of work
later.

Stored XSS vulnerability in Subversion Plugin 2.12.2:

    https://jenkins.io/security/advisory/2020-02-12/#SECURITY-1725

Update of dependencies is not needed but may save a bit of work in the
future.

**ATTENTION** -- This plugin was not defined in Puppet configuration
prior to this commit, but it was installed in our Jenkins instance
(https://jenkins.tails.boum.org).

Dangerous permissions can be configured independently of Administer
permission (in version 1.1):

    https://jenkins.io/security/advisory/2017-04-10/#matrix-authorization-strategy-plugin-allowed-configuring-dangerous-permissions

Dependencies updates are not mandatory, but may save a bit of work in
the future.

Sandbox bypass vulnerabilities in "Script Security" plugin (1.64):

    https://jenkins.io/security/advisory/2019-11-21/#SECURITY-1658
    https://jenkins.io/security/advisory/2020-02-12/#SECURITY-1713
    https://jenkins.io/security/advisory/2019-10-01/#SECURITY-1579
    https://jenkins.io/security/advisory/2020-03-09/#SECURITY-1754

Stored XSS vulnerability in Timestamper Plugin (1.10):

    https://jenkins.io/security/advisory/2020-03-09/#SECURITY-1784

Timestamper 1.11.2 (non-implied) dependencies:

    Pipeline: API ≥ 2.39
    Pipeline: Step API ≥ 2.19

"Pipeline: Step API" update is not mandatory but does no harm and may
save a bit of work in the future.

Multiple security vulnerabilities in Jenkins 2.196 and earlier, and LTS
2.176.3 and earlier:

    https://jenkins.io/security/advisory/2019-09-25/

Multiple security vulnerabilities in Jenkins 2.227 and earlier, LTS
2.204.5 and earlier:

    https://jenkins.io/security/advisory/2020-03-25/

Multiple vulnerabilities in Jenkins 2.218 and earlier, LTS 2.204.1 and
earlier:

    https://jenkins.io/security/advisory/2020-01-29/