Fixes related to whitespace for parsing "show interfaces accounting"

[jlmcgraw]

Description

• iosxe
  • Modified class ShowInterfacesAccounting
    • Modified regex pattern to support interface descriptions with multiple spaces
    • Only right-strip whitespace from lines and modify regex for lines containing counters to add explicit leading
      whitespace

Motivation and Context

learn("interface") was crashing on output from an iosxe device where interface descriptions had multiple spaces

Impact (If any)

The output that was failing now parses successfully

Checklist:

• I have updated the changelog.
• I have updated the documentation (If applicable).
• I have added tests to cover my changes (If applicable).
• All new and existing tests passed.
• All new code passed compilation.