Release version 5.0.3 with security updates and bug fixes (#1995)

- Updated golang.org/x/net from v0.35.0 to v0.37.0 for security
improvements.
- Built the plugin with Go version 1.24.1.
- Fixed basic authentication issues for Zabbix versions <7.2.
- Bumped grafana-plugin-sdk-go from v0.270.0 to v0.274.0.

.changeset/four-cobras-invent.md

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-'grafana-zabbix': patch
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-
-Security: Update golang.org/x/net from v0.35.0 to v0.37.0

.changeset/gentle-carrots-cough.md

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----
-'grafana-zabbix': patch
----
-
-Chore: Build plugin with go 1.24.1

.changeset/purple-lions-join.md

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-'grafana-zabbix': patch
----
-
-Fix: Basic authentication in zabbix <7.2

.changeset/witty-eels-camp.md

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----
-'grafana-zabbix': patch
----
-
-Chore: Bump grafana-plugin-sdk-go from 0.270.0 to 0.274.0