Fix: Unicode encoding and logging errors in lftools

Fix: Unicode encoding and logging errors in lftools

1. Fix UnicodeEncodeError in Gerrit/Nexus API requests:
   - Encode JSON string data as UTF-8 in RestApi._request()
   - Change Nexus encoding from latin-1 to utf-8 (5 locations)
   - Handles Unicode characters in responses (e.g., user names with 'š')
   - Fixes: 'latin-1' codec can't encode character '\u0161'

2. Fix logging format errors (3 locations):
   - GitHub create-repo: Use f-string instead of comma in log.info()
   - GitHub votes: Use f-string for approval list logging
   - Gerrit vote_on_change: Use f-string with parameters
   - Fixes: TypeError: not all arguments converted during string formatting

Based on: https://github.com/modeseven-lfit/lftools-uv/pull/53
Tested with: lftools gerrit addgithubrights git.opendaylight.org gnmi

Change-Id: Ief4a4ffa9bcc1d0a31342ac49b448fd097dda879
Signed-off-by: Anil Belur <abelur@linuxfoundation.org>