chore(trusted.ci.jenkins.io): ouput to generate a zip of update center env files to access file shares

[lemeurherve]

This PR adds an output with a command to generate a zip containing two env files:

• .env-content for updates-jenkins-io File Share
• .env-redirections for updates-jenkins-io-httpd File Share

This zip file has to be uploaded as zip credentials on trusted.ci.jenkins.io for the update-center2/site/publish.sh script to work.

Ref:

• feat(publish.sh): use dedicated source folder for httpd service including only .htaccess files update-center2#777
• [INFRA-3100] Migrate updates.jenkins.io to another Cloud helpdesk#2649

[lemeurherve]

Changes to Outputs:

• update_center_fileshares_env_zip_credentials = (sensitive value)

You can apply this plan to save these new output values to the Terraform
state, without changing any real infrastructure.

[dduportal]

LGTM!