docs: Label filter expression: Change unit suffix suffix to proper case whe…

[nickgrafana]

Label filter expression: Change unit suffix suffix to proper case when dealing with a Byte datatype

What this PR does / why we need it: This updates documentation to match functionality described in the source code here.

The lexer does not support lowercase units "kb" or "gb".

Please note I have removed E/PB and E/PiB and will be creating a separate issue for them as they do not seem to be supported at the time.

Which issue(s) this PR fixes: Fixes #

Special notes for your reviewer:

Checklist

• [x] Reviewed the CONTRIBUTING.md guide (required)
• [x] Documentation added
• [ ] Tests updated
• [ ] Title matches the required conventional commits format, see here
  • Note that Promtail is considered to be feature complete, and future development for logs collection will be in Grafana Alloy. As such, feat PRs are unlikely to be accepted unless a case can be made for the feature actually being a bug fix to existing behavior.
• [ ] Changes that require user attention or interaction to upgrade are documented in docs/sources/setup/upgrade/_index.md
• [ ] For Helm chart changes bump the Helm chart version in production/helm/loki/Chart.yaml and update production/helm/loki/CHANGELOG.md and production/helm/loki/README.md. Example PR
• [ ] If the change is deprecating or removing a configuration option, update the deprecated-config.yaml and deleted-config.yaml files respectively in the tools/deprecated-config-checker directory. Example PR

[grafanabot]

This PR must be merged before a backport PR will be created.

[grafanabot]

This PR must be merged before a backport PR will be created.