Add elasticsearch repository test

[puppylpg]

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1. Add elasticsearch repository test cases;
2. Fix: use LocalDate rather than String type to match the annotation @Field(type = Date). The former String type is a misuse of date type and will cause the following warn:

   WARN  org.springframework.data.elasticsearch.core.mapping.SimpleElasticsearchPersistentProperty - Unsupported type 'class java.lang.String' for date property 'date'.
   

3. Use singleton containers when testing using testcontainers;

[mp911de]

@sothawo what do you think?

[sothawo]

I will have a look, but cannot do this before the next weekend

[mp911de]

Closing as this pull request wasn't updated in time. If you would like us to look at this issue, please provide additional information and we will re-open the issue.

[puppylpg]

Sorry for the late response. The code has been modified according to the review suggestions.