Add new attribute default value to PersonSelector

[symphony-mariacristina]

Goal of this task will be to add a new optional attribute to PersonSelector Element.

Attribute name	Optional	Type	Max length	Attribute description
value	true	List of number	256	Contains the list of user IDs separated by a ',' Example:“[123]“"[123,789,654]"

Examples of usage:

• Person Selector with one selected user

<!-- MessageML -->
<messageML>
  <form id="all-elements">            
    <person-selector name="person-selector" placeholder="Type a person's name" value="[123]"/>    
    <button name="send-answers" type="action">Send Answers</button>
    <button type="reset">Reset Data</button>
  </form>
</messageML>

<!-- PresentationML -->
<div data-format="PresentationML" data-version="2.0"> 
  <form id="all-elements"> 
    <div class="person-selector" data-name="person-selector" data-placeholder="Type a person's name" date-value="[123]"></div> 
    <button type="action" name="send-answers">Send Answers</button> 
    <button type="reset">Reset Data</button> 
  </form> 
</div>

• Person Selector with multiple selected users

<!-- MessageML -->
<messageML>
  <form id="all-elements">            
    <person-selector name="person-selector" placeholder="Type a person's name" value="[123,789,654]"/>    
    <button name="send-answers" type="action">Send Answers</button>
    <button type="reset">Reset Data</button>
  </form>
</messageML>

<!-- PresentationML -->
<div data-format="PresentationML" data-version="2.0"> 
  <form id="all-elements"> 
    <div class="person-selector" data-name="person-selector" data-placeholder="Type a person's name" data-value="[123,789,654]"></div> 
    <button type="action" name="send-answers">Send Answers</button> 
    <button type="reset">Reset Data</button> 
  </form> 
</div>