#MIFOSX-1068 Option to change approved amount during loan approval

###### Features
1> Allows approver to change the approved amount, non zero and less than or equal to proposed loan amount.
2> On undo of approve, restores approved amount back.

Check list
- [x]  Integration test cases written
- [x]  Pull request has a Jira issue
- [x]  JIRA number as a part of the commit message
- [x]  Code has been formatted
- [x]  Work is present in a single commit
- [x]  Rebased on top of the latest code from develop branch
- [ ]  "gradlew licenseFormatMain licenseFormatTest licenseFormatIntegrationTest" has been run, Not,  license is manually added.
- [x]  API documentation done
@vishwasbabu why are we recomputing principal amount?, because it is available in loan abject, @pramodn02 said may be for multi-tranche loans, he is also not sure, I wanted to write comment saying that give appropriate comment at this place.