[BitSail][Feature] Support generate constant value in FakeSource

[kyle-hawk]

Signed-off-by:

Pre-Checklist

Note: Please complete ALL items in the following checklist.

• [x] I have read through the CONTRIBUTING.md documentation.
• [x] My code has the necessary comments and documentation (if needed).
• [x] I have added relevant tests.

Purpose

• close #244

Approaches

users can config constant value by defaultValue field, like this

      "columns": [
        {
          "name": "double_value",
          "type": "double",
          "defaultValue": "13.5"
        }
      ]

Related Issues

• close #244

New Behavior (screenshots if needed)

N/A