fix(entity): add argument `ignore_not_found` to ignore "not found" errors

[pranav-new-relic]

New Relic Internal

Jira

Summary

This PR proposes the addition of a new attribute ignore_not_found to the newrelic_entity data source in order to "ignore" not found errors if set true in the configuration, thereby stopping automated Terraform pipelines from halting if the entity is lost, which is useful in cases when the entity abruptly expires (see original usecase proposed by the customer in #2599).

Testing

The changes have been manually verified multifold. The test cases could not be updated because they fail with an "id" not found error, since the data source fetches no entity, which we try validating (without the expectation of an error being thrown, instead).

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 0% with 13 lines in your changes are missing coverage. Please review.

Project coverage is 33.78%. Comparing base (e6a5d8e) to head (43214e8).

Files	Patch %	Lines
newrelic/data_source_newrelic_entity.go	0.00%	13 Missing :warning:

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #2628      +/-   ##
==========================================
+ Coverage   32.83%   33.78%   +0.95%     
==========================================
  Files          98       98              
  Lines       26872    26884      +12     
==========================================
+ Hits         8824     9084     +260     
+ Misses      17890    17600     -290     
- Partials      158      200      +42     

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