Fix source command detection if we have a field expression before source

[LDrago27]

Description

The PPL grammar defines searchCommand as follows

searchCommand
   : (SEARCH)? (searchExpression)* fromClause? (searchExpression)*     # searchFrom

However when we write a query

`attributes.EnvName` = "Production" SOURCE = logs-otel-v1* 

It gives no result.

The issue lies with us appending source = at the beginning of the query.

Query Being sent:

"source = logs-otel-v1* `attributes.EnvName` = \"Production\" SOURCE = logs-otel-v1* | WHERE `time` >= '2024-06-23 17:39:57.609' AND `time` <= '2025-09-23 17:39:57.609'"

This treats the second SOURCE as a column name creating failures.

This PR fixes the Source Command detection Logic, expanding the logic to check the first | and check if it contains source = or not.

Issues Resolved

Screenshot

Testing the changes

Before:
https://github.com/user-attachments/assets/0be09f44-b271-4d3b-ba50-32261c2bde80

After:
https://github.com/user-attachments/assets/ccc9ed0a-9467-4be3-958d-81fc65afcb50

Changelog

• fix: Source command detection if we have a field expression before source

Check List

• All tests pass
  • yarn test:jest
  • yarn test:jest_integration
• New functionality includes testing.
• New functionality has been documented.
• Update CHANGELOG.md
• Commits are signed per the DCO using --signoff

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 60.25%. Comparing base (dd1f5ae) to head (c874382).
⚠️ Report is 5 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #10598      +/-   ##
==========================================
+ Coverage   60.19%   60.25%   +0.05%     
==========================================
  Files        4300     4385      +85     
  Lines      115053   116753    +1700     
  Branches    18680    19010     +330     
==========================================
+ Hits        69259    70346    +1087     
- Misses      41049    41568     +519     
- Partials     4745     4839      +94     

Flag	Coverage Δ
Linux_1	26.66% <ø> (+<0.01%)	⬆️
Linux_2	38.83% <ø> (+<0.01%)	⬆️
Linux_3	38.42% <ø> (?)
Linux_4	32.60% <100.00%> (+<0.01%)	⬆️
Windows_1	26.67% <ø> (+<0.01%)	⬆️
Windows_2	38.80% <ø> (+<0.01%)	⬆️
Windows_3	38.42% <ø> (+0.60%)	⬆️
Windows_4	32.60% <100.00%> (+<0.01%)	⬆️

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