extensions: Add extension categories in envoy_cc_extension

[phlax]

Commit Message: extensions: Add extension categories in envoy_cc_extension
Additional Description:

This is a breakout PR from #14721

atm it just marks the category as SOMECAT as a marker. I will go through and add correct categories...

Risk Level:
Testing:
Docs Changes:
Release Notes:
Platform Specific Features:
[Optional Runtime guard:]
[Optional Fixes #Issue]
[Optional Deprecated:]

[phlax]

@htuch hopefully this is doing the right thing - at least so far.

to figure out the categories i have used the following command:

$ git grep "std::string category() const override " | cut -d' ' -f9 | xargs -I{} bash -c "X={} echo \${X}" | sort | uniq
envoy.access_logger.extension_filters
envoy.access_loggers
envoy.bootstrap
envoy.clusters
envoy.compression.compressor
envoy.compression.decompressor
envoy.dubbo_proxy.filters
...

hopefully this is the ~canonical way to derive the categories.

ill start matching them now...

[phlax]

@htuch apologies for delay on this, i was fighting starlark syntax.

i think this is ready for final review.

the only one left with SOMECAT is the crypto (~not) extension

[htuch]

LGTM modulo TODOs and resolving the SSL implementation status with @lizan.

[phlax]

@htuch this should be gtg once tests have passed

[phlax]

@htuch i have added envoy.io_socket category reflecting what was in the source/extensions/extensions_build_config.bzl file

afaict there is not a factory for it tho, not sure of the implications

[lizan]

SGTM

[phlax]

/retest

[repokitteh-read-only]

Retrying Azure Pipelines:
Retried failed jobs in: envoy-presubmit

🐱

Caused by: a #14744 (comment) was created by @phlax.

see: more, trace.