Backend plugins: Renderer v2 plugin (#23625)

grafana-plugin-model is legacy and is replaced by new backend 
plugins SDK and architecture. Renderer is not part of SDK and 
we want to keep it that way for now since it's highly unlikely there 
will be more than one kind of renderer plugin.
So this PR adds support for renderer plugin v2.
Also adds support sending a Device Scale Factor parameter to the 
plugin v2 remote rendering service and by that replaces #22474.
Adds support sending a Headers parameter to the plugin v2 and
remote rendering service which for now only include 
Accect-Language header (the user locale in browser when using 
Grafana), ref grafana/grafana-image-renderer#45.
Fixes health check json details response.
Adds image renderer plugin configuration settings in defaults.ini 
and sample.ini.

Co-Authored-By: Arve Knudsen <arve.knudsen@gmail.com>

conf/sample.ini

@@ -682,6 +682,66 @@
 ;enable_alpha = false
 ;app_tls_skip_verify_insecure = false
 
+#################################### Grafana Image Renderer Plugin ##########################
+[plugin.grafana-image-renderer]
+# Instruct headless browser instance to use a default timezone when not provided by Grafana, e.g. when rendering panel image of alert.
+# See ICU’s metaZones.txt (https://cs.chromium.org/chromium/src/third_party/icu/source/data/misc/metaZones.txt) for a list of supported
+# timezone IDs. Fallbacks to TZ environment variable if not set.
+;rendering_timezone =
+
+# Instruct headless browser instance to use a default language when not provided by Grafana, e.g. when rendering panel image of alert.
+# Please refer to the HTTP header Accept-Language to understand how to format this value, e.g. 'fr-CH, fr;q=0.9, en;q=0.8, de;q=0.7, *;q=0.5'.
+;rendering_language =
+
+# Instruct headless browser instance to use a default device scale factor when not provided by Grafana, e.g. when rendering panel image of alert.
+# Default is 1. Using a higher value will produce more detailed images (higher DPI), but will require more disk space to store an image.
+;rendering_viewport_device_scale_factor =
+
+# Instruct headless browser instance whether to ignore HTTPS errors during navigation. Per default HTTPS errors are not ignored. Due to
+# the security risk it's not recommended to ignore HTTPS errors.
+;rendering_ignore_https_errors =
+
+# Instruct headless browser instance whether to capture and log verbose information when rendering an image. Default is false and will
+# only capture and log error messages. When enabled, debug messages are captured and logged as well.
+# For the verbose information to be included in the Grafana server log you have to adjust the rendering log level to debug, configure
+# [log].filter = rendering:debug.
+;rendering_verbose_logging =
+
+# Instruct headless browser instance whether to output its debug and error messages into running process of remote rendering service.
+# Default is false. This can be useful to enable (true) when troubleshooting.
+;rendering_dumpio =
+
+# Additional arguments to pass to the headless browser instance. Default is --no-sandbox. The list of Chromium flags can be found
+# here (https://peter.sh/experiments/chromium-command-line-switches/). Multiple arguments is separated with comma-character.
+;rendering_args =
+
+# You can configure the plugin to use a different browser binary instead of the pre-packaged version of Chromium.
+# Please note that this is not recommended, since you may encounter problems if the installed version of Chrome/Chromium is not
+# compatible with the plugin.
+;rendering_chrome_bin =
+
+# Instruct how headless browser instances are created. Default is 'default' and will create a new browser instance on each request.
+# Mode 'clustered' will make sure that only a maximum of browsers/incognito pages can execute concurrently.
+# Mode 'reusable' will have one browser instance and will create a new incognito page on each request.
+;rendering_mode =
+
+# When rendering_mode = clustered you can instruct how many browsers or incognito pages can execute concurrently. Default is 'browser'
+# and will cluster using browser instances.
+# Mode 'context' will cluster using incognito pages.
+;rendering_clustering_mode =
+# When rendering_mode = clustered you can define maximum number of browser instances/incognito pages that can execute concurrently..
+;rendering_clustering_max_concurrency =
+
+# Limit the maxiumum viewport width, height and device scale factor that can be requested.
+;rendering_viewport_max_width =
+;rendering_viewport_max_height =
+;rendering_viewport_max_device_scale_factor =
+
+# Change the listening host and port of the gRPC server. Default host is 127.0.0.1 and default port is 0 and will automatically assign
+# a port not in use.
+;grpc_host =
+;grpc_port =
+
 [enterprise]
 # Path to a valid Grafana Enterprise license.jwt file
 ;license_path =