Fixing pydantic validation issue of tilejson metadata

[doublebyte1]

Overview

The tileset metadata endpoint for tilejson metadata is no longer working.

Related Issue / Discussion

#1418

Additional Information

This issue is related to the upgrade of the pydantic version: #1353

According to this, pydantic2 requires all the optional fields to be present, unless they have a default value of None. This PR adds defaults values to all the optional fields, so that we continue to instantiate the model, without having all the information.

Contributions and Licensing

(as per https://github.com/geopython/pygeoapi/blob/master/CONTRIBUTING.md#contributions-and-licensing)

• I'd like to contribute [feature X|bugfix Y|docs|something else] to pygeoapi. I confirm that my contributions to pygeoapi will be compatible with the pygeoapi license guidelines at the time of contribution.
• I have already previously agreed to the pygeoapi Contributions and Licensing Guidelines

[ricardogsilva]

+1

This is a consequence of migrating to pydantic V2, where the Optional type annotation no longer makes pydantic provide an automatic intialization value of None - more info here (see the note box):

https://docs.pydantic.dev/latest/concepts/models/#required-fields

[PascalLike]

The same potential issue also here https://github.com/geopython/pygeoapi/blob/master/pygeoapi/models/provider/base.py