Add native6, OBS6 and RAWOBS rootpaths to metoffice template in config-user-example.yml and remove temporary dir

[alistairsellar]

Description

Add native6, OBS6 and RAWOBS rootpaths to metoffice config-user.yml template, and remove temporary dir. Linked Core PR: https://github.com/ESMValGroup/ESMValCore/pull/2432.

Note: This includes previous changes that were not mirrored from Core to Tool, so is beyond the strict scope of this PR, but ensures files are identical as requested in file header.

• Closes #3612

• Link to documentation: https://esmvaltool--3613.org.readthedocs.build/en/3613/

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[alistairsellar]

@valeriupredoi, since you reviewed https://github.com/ESMValGroup/ESMValCore/pull/2432, please could you review this counterpart in ESMValTool?