Add example to delete multiple measurements at once

On this page:
https://docs.influxdata.com/influxdb/cloud/write-data/delete-data/

~Describe how to~ in step 1, clarify that each `delete` command can delete from exactly one measurement. Add note to delete data from multiple measurements, use multiple `delete` commands.

In step 4, clarify the `predicate` option must use an exact name (measurement, tag key or field key) **and** an exact value to match on. (Regex not supported). For more detail, see Delete predicate syntax: https://docs.influxdata.com/influxdb/cloud/reference/syntax/delete-predicate/#delete-points-by-measurement

Open the delete-data page linked in the issue and review step 1 and step 4. Clarify that each delete command targets one measurement, add the multiple-command example guidance, and state that predicates require exact names and values; compare the result with the linked delete predicate syntax reference.

Written by the indexing model from the issue text.