Improvements to influxd upgrade command

[stuartcarnie]

What

In order to improve the upgrade experience for users moving from 1.x to 2.x, the following improvements should be added to the influxd upgrade command:

• If the meta.db contains existing continuous queries, these should be written out to a separate file, continuous_queries.txt. This path should be available as a flag that can be changed, with a default value along side the upgrade.log

• If the influxdb 1.x configuration file has disabled HTTP authentication and has users, this should be logged as a warning.

  # Determines whether HTTP authentication is enabled.
  # auth-enabled = false
  

Disabled HTTP authentication

If this feature is disabled in InfluxDB 1.x, clients sending requests with credentials are ignored by influxd. This may result in failures after upgrading for the following reasons:

• If the 1.x instance has users and 1.x clients, such as telegraf, are sending credentials, they will be silently ignored by InfluxDB 1.x
• Once upgraded to 2.x, those clients' requests will now be authorised by influxd 2.x and fail with a 401 Unauthorized response if the credentials do not match.

NOTE: We may wish to alter the upgrade process in future, such that if HTTP auth is disabled, the users are not copied to 2.x.

[danxmoran]

I would also like to add:

• Move as many input validations as possible to the beginning of execution (i.e. input paths pointing to nonexistent files, output paths pointing to existing files)

[danxmoran]

Closed in #20012 #20036 #20039