[text_service]Prevent pylint to check signatures

When having a base class and a derived class, pylint can complain
because some methods have the same signatures. In particular, this
happens if the function signature spans more than 4 rows, triggering
the similarity checker. This is the case for the function
lemmas_frequency.
I disable this pylint feature.

For more info: pylint-dev/pylint#3619

services/text_service/pyproject.toml

@@ -17,3 +17,6 @@ black = "^21.12b0"
 [build-system]
 requires = ["poetry-core>=1.0.0"]
 build-backend = "poetry.core.masonry.api"
+
+[tool.pylint."SIMILARITIES"]
+ignore-signatures="yes"