Update to latest ubuntu image in dockerfile to avoid lots of vulnerabilities

[1stvamp]

Bump Dockerfile to use ubuntu:mantic-20231011 for its base image to reduce the number of vulnerable libraries/packages installed with the image.

Note: This relates to an internal developer productivity issue; I will link this issue from there.

Checklists

Pre-Review Checklist

• Covered the changes with automated tests
• Tested the changes locally
• Added a label for each target release version (example: v7.13.2, v7.14.0, v8.0.0)
• Considered corresponding documentation changes
• Contributed any configuration settings changes to the configuration reference

For Elastic Internal Use Only

• Considered corresponding documentation changes to contribute separately
• New configuration settings added in this PR follow the official guidelines
• Built gems (both connectors_utility and connectors_service) and included into Enterprise Search and tested that Enterprise Search works well with new gem versions. Instruction can be found here

[1stvamp]

Still need to test the gems in Enterprise Search.

[1stvamp]

Double checked that the docker change doesn't affect building connectors_utility gem, so we're good on that front 👍

[github-actions]

💔 Failed to create backport PR(s)

Status	Branch	Result
❌	8.12	The branch "8.12" is invalid or doesn't exist

To backport manually run:
backport --pr 588 --autoMerge --autoMergeMethod squash