`aem.events_osgi_mapping` enrich xdm Asset to add DamAsset metadata

The challenge would be in white-listing the metadata, as it can be too large.

it could be like this:

```
package package com.adobe.aio.aem.event.xdm.aem;

import com.adobe.xdm.assets.Asset;
import com.fasterxml.jackson.annotation.JsonIgnore;
import com.fasterxml.jackson.annotation.JsonIgnoreProperties;
import com.fasterxml.jackson.annotation.JsonInclude;
import com.fasterxml.jackson.annotation.JsonInclude.Include;
import com.fasterxml.jackson.annotation.JsonProperty;
import java.util.GregorianCalendar;
import java.util.HashMap;
import java.util.Map;
import java.util.Objects;
import org.apache.sling.api.resource.ValueMap;

@JsonInclude(Include.NON_NULL)
@JsonIgnoreProperties(ignoreUnknown = true)
public class DamAsset extends Asset {

Map metadatas;

@JsonIgnore
public void setMetadata(ValueMap valueMap) {
if (valueMap != null) {
metadatas = new HashMap<>();
for (String entry : valueMap.keySet()) {
Object value = valueMap.get(entry);
if (value != null && !entry.startsWith("jcr:") && !(value instanceof GregorianCalendar)
&& !(value.getClass().isArray())) {
metadatas.put(entry, value.toString());
//TODO better filtering with metadata whitelist configuration
}
}
}
}

@JsonProperty("xdmAsset:metadatas")
public Map getMetadata() {
return metadatas;
}

@Override
public boolean equals(Object o) {
if (this == o) {
return true;
}
if (o == null || getClass() != o.getClass()) {
return false;
}
if (!super.equals(o)) {
return false;
}
DamAsset damAsset = (DamAsset) o;
return Objects.equals(metadatas, damAsset.metadatas);
}

@Override
public int hashCode() {
return Objects.hash(super.hashCode(), metadatas);
}

@Override
public String toString() {
return "DamAsset{id='" + this.id + '\'' + ", type='" + this.type + '\'' + ", assetId='"
+ this.getAssetId() + '\'' + ", assetName='" + this.getAssetName() + '\''
+ ", etag='" + this.getEtag()
+ '\'' + ", path='" + this.getPath() + '\'' + ", format='" + this.getFormat() + '\''
+ "metadatas=" + metadatas +
'}';
}
}

```

首先定位 aem.events_osgi_mapping 的实现以及现有的 XDM Asset 映射入口点。检查如何获取 AEM 资产元数据，然后定义 issue 中描述的元数据白名单和 DamAsset 映射。完成的标准是 XDM asset 包含允许的 DamAsset 元数据，同时不包含过大的值或被排除的值。

由索引模型根据 Issue 内容生成。