Edit MediaSample.java for MediaQuery with CollectionId

[enveryasar]

Description

Adds sample usage and documentation for the collectionId parameter in MediaQuery.

Changes

• MediaSample.java: Added example demonstrating media filtering by collection ID
• README.md: Updated documentation to reflect the new filtering capability

Testing

Manually tested - filtering works correctly:

• Without collectionId: Returns all media from portal
• With collectionId: Returns only media from specified collection

Example

MediaQuery query = new MediaQuery()
    .setCollectionId("collection-id")
    .setLimit(10);

[coveralls]

coverage: 40.081%. remained the same
when pulling 24eb461 on API-2675
into 700d939 on master.