T9273: Add Telegraf global_tags option configurable

Adds Telegraf global_tags support - static tags stamped onto every metric.

```
set service monitoring telegraf global-tag <tag-name> value <tag-value>
```
Rendered as a [global_tags] block in telegraf.conf, applied ahead of all outputs.

1 files changed, 6 insertions, 0 deletions

diff --git a/src/conf_mode/service_monitoring_telegraf.py b/src/conf_mode/service_monitoring_telegraf.py
index 9ce73eaf8..24571aa96 100755
--- a/src/conf_mode/service_monitoring_telegraf.py
+++ b/src/conf_mode/service_monitoring_telegraf.py
@@ -126,6 +126,12 @@ def verify(monitoring):
 
     verify_vrf(monitoring)
 
+    # Verify global-tag
+    if 'global_tag' in monitoring:
+        for tag, tag_config in monitoring['global_tag'].items():
+            if 'value' not in tag_config:
+                raise ConfigError(f'Global tag "{tag}" has no value assigned!')
+
     # Verify influxdb
     if 'influxdb' in monitoring:
         if 'authentication' not in monitoring['influxdb'] or \