Appgate SDP implementation and metadata (#18465)

* created file structure

* added metrics.py

* add openmetricsv2 class and options

* add README

* add caddy and docker-compose

* caddy container doesn't start

* todo: add fixtures metrics file

* added fixtures and metric file

* add configuration spec

* conf.yaml git add appgate_sdp/datadog_checks/appgate_sdp/data/conf.yaml.example

* edits to conf.yaml

* fix config files

* metrics

* works

* add metrics from 6.3.3

* edits to metrics.py

* added metadata.csv

* linted

* updated metrics in fixtures to metrics from v.6.4

* updates metrics.py to add metrics from v6.4

* ddev validate ci and some fixes

* sync models

* remove non existent dashboard ref to fix CI validation

* fix appgate_sdp import

* fix manifest.json

* fix license headers

* fix metric names

* remove empty dashboard entry

* fix configuration and metadata.csv

* fix metadata.cvs and unit tests

* add orientation

* fix entry in metadata.csv

* add labeler.yaml

* point dockerfile to correct file path

* add metric to check

* fix E2E

* add to service_check.json

* add integration link to readme

* revert changed root README template

* revert changed root README template

* add unit_names to metadata and update changelog PR number

* more unit names

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Co-authored-by: Kyle-Neale <[email protected]> d9754e1