feat: Add and remove influence

[Bonjemus]

Description

Describe the changes
It seemed pretty weird to me that those functions weren't here in the first place.

What is the current behavior? (You can also link to an open issue here)

What is the new behavior? (if this is a feature change)

Does this PR introduce a breaking change? (What changes might users need to make in their application due to this PR?)
No.

Other information:

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)
• Documentations

Submission checklist

• I have checked the project can be compiled
• I have tested my changes and it worked as expected

Patches (if there are any changes related to Harmony patches)

• I have checked no IL patching errors in the console

Other

• Still requires more testing

[YongAn404]

You can add these two together as well

    /// <summary>
    /// Get influence to a given <see cref="Faction"/>.
    /// </summary>
    /// <param name="faction">The <see cref="Faction"/> to get influence.</param>
    /// <returns>Get the faction influence..</returns>
    public static float GetInfluence(Faction faction)
    {
        return FactionInfluenceManager.Get(faction);
    }

    /// <summary>
    /// Set influence to a given <see cref="Faction"/>.
    /// </summary>
    /// <param name="faction">The <see cref="Faction"/> to set influence.</param>
    /// <param name="influence">The amount of influence to set.</param>
    public static void SetInfluence(Faction faction, float influence)
    {
        FactionInfluenceManager.Set(faction, influence);
    }

[Bonjemus]

Done. 👍

[VALERA771]

Everytring can be inlined