Gracefully catch tile not found

[webb-ben]

Overview

This PR introduces graceful catching of Not Found errors for a Tile provider. When a Tile provider raises ProviderTileNotFoundError the API returns a 404 gracefully.

Related Issue / discussion

#1936

Additional information

Willing to adapt the solution - but if the expected behavior is to return a 404, I think it does make sense to not log such behavior as an error.

Dependency policy (RFC2)

• I have ensured that this PR meets RFC2 requirements

Updates to public demo

• I have ensured that breaking changes to the pygeoapi master demo server have been addressed
  • https://github.com/geopython/demo.pygeoapi.io/blob/master/services/pygeoapi_master/local.config.yml

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