enhance support for limits (RFC5)

[tomkralidis]

Provide enhanced limit handling implementation in support of better definition and control on data query limiting.

RFC5 can be found at https://pygeoapi.io/development/rfc/5.

[webb-ben]

@Youssef-Harby @tomkralidis bringing part of the conversation about "unlimited" defaultitems configuration in pygeoapi. Given the relative heterogeneity of providers, I wonder if it possible to realistically implement that on a provider level. At least I wonder if the most effective implementation would leverage the hits response and then querying by the literal limit. For various systems that interact with pygeoapi, this is generally the behavior I do to get "all" the items returned. See
https://github.com/cgs-earth/pygeoapi-plugins/blob/dc7fb55a2126c6a178c71e2097f1066ba35fd12b/pygeoapi_plugins/process/intersect.py#L192-L193

Is there a way to do this without consistently making two queries on a provider, first effectively getting resulttype=hits and then second with that value? Is there a naive way to pass python infinity to providers?

[webb-ben]

Interestingly, if we changed https://github.com/geopython/pygeoapi/blob/master/pygeoapi/util.py#L147 to

        if '.' in value or 'inf' in value:  # float?

you could get pygeoapi to cast the configured defaultlimit to pythonic infinity, and it works for at least some of the providers. At the moment this is only possible if you set this as an environment variable, but its not that far off.

    limits:
        default_items: ${PYGEOAPI_SERVER_DEAULT_LIMIT:-inf}