Update contextual help for date format in page providers

Current help does not provide anything helpful:

Define the format of the returned value. For example, 'yyyy' returns a formatted value like '2013', '2014', etc. See 'date histogram aggregation' section from Elasticsearch documentation.

Update to:

DATE RANGE AGG

Define how dates are formatted, e.g. MM/dd/yyyy (month/day/year). Detailed options are available in the (elasticsearch documentation)https://www.elastic.co/guide/en/elasticsearch/reference/current/search-aggregations-bucket-daterange-aggregation.html#date-format-pattern

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DATE HISTOGRAM AGG

Define how dates are formatted, e.g. yyyy for year, MM / MMMMM for month (number / letters), dd for day. Detailed options are available in the (elasticsearch documentation)https://www.elastic.co/guide/en/elasticsearch/reference/current/search-aggregations-bucket-daterange-aggregation.html#date-format-pattern

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