GH-475 Add config migrations

[vLuckyyy]

I plan to merge this only AFTER the first release.

This pull request introduces a migration system within the configuration. The purpose of this system is to facilitate easy key changes in the configuration while maintaining compatibility with older data.

Here's an example of a migration:

package com.eternalcode.core.configuration.migration.impl;

import com.eternalcode.core.configuration.migration.AbstractMigration;

import static com.eternalcode.core.configuration.migration.MigrationStep.move;

public class PC1 extends AbstractMigration {

    public PC1() {
        super("Cosmetic change for number of lines to clear.",
            move("chat.linesToClear", "chat.numberOfLinesToClear"));
    }

    @Override
    public int migrationNumber() {
        return 1;
    }

    @Override
    public String file() {
        return "config.yml";
    }
}

In the above example, "PC" stands for "PluginConfiguration," and "1" is the migration number. The same convention will be applied to other migrations as well.

⚠ It's worth noting that the migration system itself is in its early development stages and will likely require numerous refinements to achieve optimal functionality.

2023-08-23.13-12-04.mov

[Jakubk15]

Looks good to me overall

[Jakubk15]

Are you sure that this name isn’t too generic? We should use something more understandable.

[Rollczi]

You can base order of migrations on list order. #475 (comment)

[Rollczi]

I mean this list ^

[vLuckyyy]

I want migrate to okaeri-configs for built-in migrations and better yaml parsing.