Improve example for Polar projection

[yvonnefroehlich]

Description of proposed changes

Correspoinding to #2058 (review) and #2058 (comment) this PR aims to improve the example for the Polar projection.

• Add description of single plots (instead of #--------------)
• Set titles via -t modifier of frame parameter (instead of pygmt.Figure.text method)

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.

Slash Commands

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

• /format: automatically format and lint the code
• /test-gmt-dev: run full tests on the latest GMT development version

[yvonnefroehlich]

/format

[yvonnefroehlich]

I added noqa:W605 to allow for the escape sequence \z within the title (see b9e2d8d). But I feel this is not an optimal solution, as users might be confused by seeing this as an comment in the example code.

[seisman]

I think this PR is in great and "WIP" can be removed from the title. @yvonnefroehlich What do you think?

[yvonnefroehlich]

I think this PR is in great and "WIP" can be removed from the title. @yvonnefroehlich What do you think?

I am not totally sure. I understand the comment by @maxrjones in the way that descriptive titles should be added for the single subplots. Until now, I only wrote the positions. But maybe these are enough, as there are already quite detailed comments and titles would at least partly repeat the comments?