feat: allow filtering of emails in http endpoint

[madflow]

• This PR allows simple filtering in the HTTP endpoint /email
• Use case is - when using in CI (Cypress E2E), it can be useful to only fetch specific emails. Also Retrieve emails by subject - RestAPI #330
• You can only find emails, which correspond exactly to the query parameters.
• Nested fields in the payload can be addressed with a (to.name, headers.x-some-header) dot syntax

http http://localhost:1080/email\?to.name\="Johnny Utah"\&subject\="The ex-presidents are surfers"

[kowalczyka]

Hello,
does this change allows filtering only for endpoint in REST API or does it also affects Web UI?

[madflow]

Hello,
does this change allows filtering only for endpoint in REST API or does it also affects Web UI?

Only for simple filtering in the HTTP endpoint /email.

[pdobrosi]

I also wanted to implement the same feature :) , I like your solution.

[codecov-commenter]

Codecov Report

Merging #334 (1276862) into master (96248f8) will increase coverage by 1.24%.
The diff coverage is 96.29%.

❗ Current head 1276862 differs from pull request most recent head 1403818. Consider uploading reports for the commit 1403818 to get more accurate results

@@            Coverage Diff             @@
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+ Coverage   66.83%   68.07%   +1.24%     
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  Files          10       10              
  Lines         588      614      +26     
  Branches      125      131       +6     
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+ Hits          393      418      +25     
- Misses        195      196       +1     

[soulteary]

This feature looks very useful, I agree with @pdobrosi .

But the current code seems to have some conflicts, I will perform functional verification and resolve conflicts in a private fork. #389

If everything works, your name will appear in the v2.0.2 version, as a contributor, please continue to submit and play together @madflow

@kowalczyka webui need update, we can talk it at #381