Support adding/removing source STORED_MUSIC

[gmuth]

STORED_MUSIC is a local source type that can be added via the SoundTouch App. Bose marge also manages these sources.

In my device Sources.xml I have:

    <source displayName="fritzboxmedia" secret="" secretType="token">
        <sourceKey type="STORED_MUSIC" account="fa095ecc-e13e-40e7-8e6c-3810d5245786/1" />
    </source>

The server is also listed in /listMediaservers.
The source supports live-streams and is presetable!

---

POST /streaming/account/{accountid}/source

<?xml version="1.0" encoding="UTF-8" ?>
<source>
  <credential></credential>
  <username>fa095ecc-e13e-40e7-8e6c-3810d5245786/1</username>
  <sourceproviderid>7</sourceproviderid>
  <sourcename>fritzmedia-1</sourcename>
</source>

should return http response

201 Created
location: http://streamingqa.bose.com/account/{accountid}/source/31853908

<?xml version="1.0" encoding="UTF-8" standalone="yes"?>
<source id="31853908" type="Audio">
    <createdOn>2026-03-08T21:20:55.017+00:00</createdOn>
    <credential type="token"></credential>
    <name>fa095ecc-e13e-40e7-8e6c-3810d5245786/1</name>
    <sourceproviderid>7</sourceproviderid>
    <sourcename>fritzmedia-1</sourcename>
    <sourceSettings/>
    <updatedOn>2026-03-08T21:20:55.017+00:00</updatedOn>
    <username>fa095ecc-e13e-40e7-8e6c-3810d5245786/1</username>
</source>

---

DELETE /streaming/account/{accountid)/source/31853908

should return http response

200 OK (empty body)