fix: Added CustomLongTextField and using it for 'Expression', 'Sasl Jaas Config' fields

[shivamG640]

Fixes #1043

However there are some issues with this new CustomLongTextField listed Following:

1. The new field is interacting with the CSS of CustomNestField's ExpandableSection. Hence it doesn't load correctly for Kafka's Sasl Jaas Config:
   
   Note that once the field is click and you start adding some text, the field automatically corrects. Also the field loads correctly if we load the ExpandableSection as Expanded by adding the isExpanded attribute always.

2. The field is unable to load the form as soon as you choose any language for the Expression to configure a setBody.