ENH: Add axis attribute to 1-D latitude and longitude coordinates

[DWesl]

Description

Add the axis attribute to identify 1-D dimension coordinates already provided by cfgrib.
This attribute is recommended at the end of CF section 4:
https://cfconventions.org/Data/cf-conventions/cf-conventions-1.12/cf-conventions.html#coordinate-types

Contributor Declaration

By opening this pull request, I affirm the following:

• All authors agree to the Contributor License Agreement.
• The code follows the project's coding standards.
• I have performed self-review and added comments where needed.
• I have added or updated tests to verify that my changes are effective and functional.
• I have run all existing tests and confirmed they pass.