Add appsec.blocked tag to span

[GustavoCaso]

What does this PR do?

Make sure to add the appsec.blocked at the span when the request has been blocked.

The main change is on the different watcher files:

if span
  span.set_tag('appsec.blocked', 'true') if result.actions.include?('block')
  span.set_tag('appsec.event', 'true')
end

The line span.set_tag('appsec.blocked', 'true') if result.actions.include?('block') is the one adding the tag.

The rest of the changes are improving the codebase:

• Added Event.build_service_entry_tags helper method to reduce the size of Event.record_via_span
• Extract the shared examples for our integration specs to a separate file so they can be reuse by all the rack integrations specs

Motivation

Make sure our code is up to date with RFCs and system tests

Additional Notes

How to test the change?

CI

[codecov-commenter]

Codecov Report

Merging #2895 (17b4d92) into master (5af21bc) will decrease coverage by 0.02%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master    #2895      +/-   ##
==========================================
- Coverage   98.10%   98.09%   -0.02%     
==========================================
  Files        1266     1267       +1     
  Lines       70140    70000     -140     
  Branches     3186     3194       +8     
==========================================
- Hits        68813    68664     -149     
- Misses       1327     1336       +9     

see 14 files with indirect coverage changes

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[lloeki]

LGTM, save for a bit about naming that would bring confusion to future readers.