Inserting icon inside the input text is not working

### Issue type

**I'm submitting a ...** (check one with "x")

* [ ] bug report
* [x] feature request

### Issue description
Icon couldn't display inside the input , as per the nebular docs I have done this. No css added.
**Current behavior:**

Icon present outside of the input in the left side

**Expected behavior:**

Icon should be present inside of the input

**Steps to reproduce:**

**Related code:**

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### Other information:

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**Angular, Nebular**
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