Parquet batch configuration and documentation for spec updates

[C-Loftus]

Overview

When using the parquet provider, previously there was no config option for batch_size or batch_readahead. pyarrow defaults to batch sizes of over 100k with a default readahead of 16 batches. This is fine for analytics but in a server use case it is generally far too large and when using parquet over s3, adds a lot of extra data transfer.

I changed the provider to allow these options to have smaller defaults and to allow them to be configurable in the provider definition.

I added comments for documentation for this in the code and in the rst docs. I brought some extra info for the docs from #2271 as well while I was at it.

Related Issue / discussion

Sorta #2271 / #2150

Additional information

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