bulker errors are not ecs complient

[michel-laterman]

Some bulker errors are not ecs complient.
For example the bulker.flushRead: Error in mget request result to Elasticsearch call uses .Str("err", ERROR-STRING) which results in the resulting document with an err attribute where error.message is expected.

Occurs in many of the bulk/op*.go files

grep -r \"err\" .
./internal/pkg/bulk/opBulk.go:		log.Error().Str("mod", kModBulk).Str("err", res.String()).Msg("Fail BulkRequest result")
./internal/pkg/bulk/opApiKey.go:			log.Error().Str("err", "request too large").Msg("No API Key ID could fit request size for bulk update")
./internal/pkg/bulk/opApiKey.go:				log.Error().Str("err", res.String()).Msg("Error in bulk API Key update result to Elasticsearch")
./internal/pkg/bulk/opRead.go:		log.Warn().Str("mod", kModBulk).Str("err", res.String()).Msg("bulker.flushRead: Error in mget request result to Elasticsearch")
./internal/pkg/bulk/opSearch.go:		log.Warn().Str("mod", kModBulk).Str("err", res.String()).Msg("bulker.flushSearch: Fail writeMsearchBody")