Add supported type tests to min aggregation

[csoulios]

PR that adds tests for supported ValuesSourceTypes for the MinAggregator

[elasticmachine]

Pinging @elastic/es-analytics-geo (:Analytics/Aggregations)

[polyfractal]

👍

[andyb-elastic]

LGTM

Not sure if we want to do this or not, but in files like this one where there are some existing tests for unsupported types, I've been removing them, e.g.

elasticsearch/server/src/test/java/org/elasticsearch/search/aggregations/metrics/MinAggregatorTests.java

Lines 281 to 295 in 39785eb

	public void testUnsupportedType() {
	MinAggregationBuilder aggregationBuilder = new MinAggregationBuilder("min").field("not_a_number");
	MappedFieldType fieldType = new KeywordFieldMapper.KeywordFieldType();
	fieldType.setName("not_a_number");
	fieldType.setHasDocValues(true);
	IllegalArgumentException e = expectThrows(IllegalArgumentException.class,
	() -> testCase(aggregationBuilder, new MatchAllDocsQuery(), iw -> {
	iw.addDocument(singleton(new SortedSetDocValuesField("string", new BytesRef("foo"))));
	}, (Consumer<InternalMin>) min -> {
	fail("Should have thrown exception");
	}, fieldType));
	assertEquals(e.getMessage(), "Expected numeric type on field [not_a_number], but got [keyword]");
	}