Rework config fixtures

[jenshnielsen]

Replace existing config fixtures with 2 auto use fixtures.

• A session fixture that makes sure that we load the default config and do not read / write config from any user folder. This makes sure that we dont fail tests due to config changes of the user or modify user configs. Also let this handle setting changes that we want to be different from the default. Disable telemetry, disable subscribers, set db path to a non existing file so test can't write to the default db if not using dataset / experiment fixtures.
• A function fixture that resets any modification that a test has made to the config, closes any instruments and resets the default station

Since these are auto use we can remove all explicit use of config fixtures.

In the process fix some issues.

• The old default_config fixture would replace qc.config with a new config object. This however will not work if the test had already imported the config object as from qcodes import config so instead patch the existing config object.
• some dond tests were not correctly using the experiment fixture. This is also fixed.
• remove deprecated function
• config tests no longer needs to be skipped when running from user home as we patch the location of user home automatically before the test runs
• Fix some logging tests that were leaking state or depending on leaked state

[codecov]

Codecov Report

Merging #4906 (3d69c69) into master (c7cce2e) will not change coverage.
The diff coverage is 100.00%.

@@           Coverage Diff           @@
##           master    #4906   +/-   ##
=======================================
  Coverage   68.24%   68.24%           
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  Files         341      341           
  Lines       29901    29901           
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  Hits        20405    20405           
  Misses       9496     9496