requester: add support for persisting tabs in session database

[Warxim]

Hello, I would like to add support for persisting Requester tabs in session database, so that we do not loose them every time we restart Zaproxy.

Solution summary:

• Created table "REQUESTER_TAB" for persisting tabs.
• Added support for serializing Message data and storing them as JSON.
• Added support for deserializing JSON to Message.
• Created wrapper to handle persistance logic for ManualHttpRequestEditorPanel. (Store message change when it is sent or added to the editor.)
• Refactored tabbed pane (and related classes) to make them more simple and easily integrable with persistence logic.

[Warxim]

Applied spotlessApply

[Warxim]

Resolved conflicts (rebase)

[Warxim]

@thc202 Hello, will you please look on this PR?

[thc202]

I will once the main release is out.

[thc202]

All classes that are not intended to be used by other add-ons (IMO all being added) should be placed under the internal package, to make that clear.

The pull request needs to be rebased.

[Warxim]

Moved classes under the internal package.

[Warxim]

Rebased onto current main.

[Warxim]

Sorry for so many force pushes, noticed that my changelog line was moved to "7.0.0" section during the rebase. Moved it back to unreleased section.

[Warxim]

Added @SuppressWarnings("serial") to UI classes, because of the failing build (18).

[Warxim]

@thc202 Hello, can I help somehow, so that this PR can be approved and merged?

[Warxim]

Rebased onto current main and resolved new conflicts. It is ready for review.