only drop scheme for file type messages

[gerritholl]

Limit removing the scheme from the URI to incoming messages of type 'file'.

• Fixes segment_gatherer skips dataset messages when all_files_are_local is set #160
• Tests added
• Documentation added

[coveralls]

Pull Request Test Coverage Report for Build 12711822012

Details

• 1 of 1 (100.0%) changed or added relevant line in 1 file are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage remained the same at 90.775%

---

Totals
Change from base Build 11931253671:	0.0%
Covered Lines:	4113
Relevant Lines:	4531

---

💛 - Coveralls

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 91.78%. Comparing base (afb6cae) to head (4f2a044).
Report is 1 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #161   +/-   ##
=======================================
  Coverage   91.78%   91.78%           
=======================================
  Files          28       28           
  Lines        4005     4005           
=======================================
  Hits         3676     3676           
  Misses        329      329           

Flag	Coverage Δ
unittests	91.78% <100.00%> (ø)

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[gerritholl]

...although with the simultaneously published pytroll/pytroll-watchers#44 we don't really need it anymore...