Allow defaults per profile

Currently there is no way to set any default value for custom fields included in a profile. You can only do so at the custom field level, but the same default value will be set for all the profiles in which this custom field is included.

Implementation:
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Add a field 'default_value' to table civicrm_uf_field that would function in a similar way as the one in civicrm_custom_field.
On New/Edit Profile Field we can have 'Default Value' textbox in which default value can be entered or selected in the case of an option list.

We can also try to have Default Value be like a preview field so what you save is what you get to see as defaults in create mode.