[$40] Phase description must allow empty or null values instead of space string

[mirzailhami]

Expected behavior

Optionally allow phase description to be empty or null at API endpoint for phases patch request.

Actual behavior

Does not allow phase description to be empty or null at API endpoint. Now in the FE, we use space string to allow empty description but it will need to be updated later (based on this).

Steps to reproduce the problem

1. Add New Phase
2. Enter title
3. Select Start Date & End Date
4. Leave the description empty
5. Save Draft

Screenshot/screencast

[vikasrohit]

@mirzailhami we need changes in tc-project-service (some where here and in Connect app both for this. Issue assignee might have to create PRs for the both repos if required. It all depends on the solution created by the assigned, all we want is to get rid of the workaround of passing empty spaces.