Improved Error Messages on Client-Side Errors

[johannesduesing]

Reason for this PR
As reported in #34, the error messages returned by the webapi in cases of invalid queries / invalid query limits / errors during database interaction have all been 500 Internal Server Errors, and even exposed some application internals.
This implies that regular users may not understand the cause for a query failure, and malicious users may learn something about private data.

Changes in this PR
Introduced distinct HttpResonses on different errors:

• If the execution of an ElasticSearch query fails due to an unknown reason, a 500 Internal Server Error will be returned. The StatusDescription will contain a JSON object holding a msg ("Database Communication Failed") and a query field, the latter holding the original query that triggered the error.
• If the maximum query limit (10000) is exceeded by the client, then a 400 Bad Request is returned. The StatusDescription also holds the aforementioned JSON object, with the msg stating that the limit has been exceeded, including the value of the limit.
• If the query could not be parsed, a 400 Bad Request is returned. The StatusDescription also holds the aforementioned JSON object, with the msg explaining that there was a syntax error in the query, including the line and column of the error.
• If the query Syntax was valid but contained unknown field names, a 400 Bad Request is returned. The StatusDescription also holds the aforementioned JSON object. The msg states that there were unknown field names, and an additional attribute invalid_fields holds an array of all invalid field names.
• All other (unexpected) errors will results in a 500 Internal Server Error

Additional Context
A upcoming PR for the delphi-cli will introduce support for the 400 Bad Request responses, which will then print the error messages in order to explain search errors to the user. EDIT: PR is at delphi-hub/delphi-cli#46

Issues

• Partially addresses Search API provides internal on elastic search errors #34

[sonarqubecloud]

Kudos, SonarCloud Quality Gate passed!

0 Bugs
0 Vulnerabilities (and 0 Security Hotspots to review)
0 Code Smells

No Coverage information
0.0% Duplication

[johannesduesing]

@bhermann Can you look at this and tell me if you're fine with the changes i introduced?

[bhermann]

That look good to me!