Non standard id property

[ClintGood]

Closes #797

Draft PR

This adds support for an [Id] attribute. This can decorate a property of an entity, allowing it to use a name other than "Id"
If an Id property is not specified, it will fallback to the standard "Id" property

To support for HasManyThrough relationships with foreign key property names other than "EntityNameId", the [HasManyThrough] attribute may specify LeftIdPropertyName and RightIdPropertyName values. If not specified it will fallback to standard "EntityNameId"

A number of additional entities in the JsonApiDotNetCoreExample demonstrate these features
Player, Team, TeamPlayer, Award, PlayerAward, Championship, demonstrate HasOne, HasMany and HasManyThrough using non standard key property names.

public class Player: IIdentifiable<Guid>
{
    // Non standard id property
    [Id]
    public Guid PlayerId { get; set; }

    // Non standard HasManyThrough related property names
    [NotMapped]
    [HasManyThrough(nameof(PlayerAwards), nameof(PlayerAward.RecipientNo), nameof(PlayerAward.AwardNo))]
    public ISet<Award> Awards { get; set; }
    public ISet<PlayerAward> PlayerAwards { get; set; }
     ...

Be gentle. First PR. Constructive criticism appreciates. Based on bart-degreed:complex-queries. Only a modest number of changes if that is accepted first.

FEATURE

• write tests that address the requirements outlined in the issue
• fulfill the feature requirements
• bump package version

RELATED REPOSITORY UPDATES

• does this feature require documentation? if so, open an issue in the docs repo
• does this feature break an API that is implemented in the templates repository? if so, open an issue