Tutorial and Intro for Figure.grdcontour: Adjust line length and parameter order

[yvonnefroehlich]

Description of proposed changes

This PR improves the tutorial examples/tutorials/advanced/contour_map.py and the intro examples/get_started/02_contour_map.py:

• Use complete line length in comments and code blocks (see comment Figure.grdcontour: Deprecate parameter "interval" to "levels" (FutureWarning since v0.12.0, will be removed in v0.16.0) #3209 (comment))
• Set grid as the first parameter in Figure.grdcontour (see comment Figure.grdcontour: Deprecate parameter "interval" to "levels" (FutureWarning since v0.12.0, will be removed in v0.16.0) #3209 (comment))

Reminders

• Run make format and make check to make sure the code follows the style guide.
• Add tests for new features or tests that would have caught the bug that you're fixing.
• Add new public functions/methods/classes to doc/api/index.rst.
• Write detailed docstrings for all functions/methods.
• If wrapping a new module, open a 'Wrap new GMT module' issue and submit reasonably-sized PRs.
• If adding new functionality, add an example to docstrings or tutorials.
• Use underscores (not hyphens) in names of Python files and directories.

Slash Commands

You can write slash commands (/command) in the first line of a comment to perform
specific operations. Supported slash command is:

• /format: automatically format and lint the code