write labels to clickhouse

[dinmukhamedm]

• Write label values to clickhouse whenever we write them to Postgres
• Similarly delete label values from clickhouse when deleted from Postgres
• Fix adding a label with 0 value key (frontend)
• Fix frontend warning about <p> in <DialogDescription> which internally is a <p> as well

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[!IMPORTANT] This PR adds functionality to write and delete label values in Clickhouse alongside Postgres, fixes frontend label validation, and addresses a UI warning.

• Behavior:
  • Write label values to Clickhouse in insert_or_update_label() in labels/mod.rs and record_labels_to_db() in traces/utils.rs.
  • Delete label values from Clickhouse in delete_span_label() in routes/labels.rs.
  • Fix frontend validation for label value existence in add-label-popover.tsx.
  • Fix frontend warning about nested <p> tags in evaluator-editor-dialog.tsx.
• Database:
  • Add labels table to Clickhouse in 001000-initial.sql.
• Misc:
  • Remove unused import in datasets.rs.

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