Update name legacy api password

[balloob]

Description:

It's confusing that the legacy API password user is called 'homeassistant'. This will rename it to "Legacy API password user". This will only impact new users.

CC @awarecan

Checklist:

• The code change is tested and works locally.
• Local tests pass with tox. Your PR cannot be merged unless tests pass

If the code does not interact with devices:

• Tests have been added to verify that the new code works.