severity_parser: update docs to correct overwrite_text name

[davispuh]

I was wondering why severity_parser wasn't updating severity_text
Turns out documentation is wrong and overwrite_text is correct name for this functionality.

[linux-foundation-easycla]

The committers listed above are authorized under a signed CLA.

• ✅ login: davispuh / name: Dāvis (129b067)
• ✅ login: djaglowski / name: Daniel Jaglowski (7afeea9)

[djaglowski]

Closing in favor of the #36103

[davispuh]

#36103 is not a superset of this PR. There is additional place where wrong name is used which is fixed with this PR. See https://github.com/open-telemetry/opentelemetry-collector-contrib/blob/main/pkg/stanza/docs/operators/severity_parser.md

I'm just very lazy and edited it with GitHub UI and that's why 2 PRs because changed 2 separate files.

[monoxono]

Hi @djaglowski, as @davispuh said, the fix in this PR is in file pkg/stanza/docs/operators/severity_parser.md and it's different from #36103 where pkg/stanza/docs/types/severity.md got fixed.
Could you please check it? Thanks.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 81.18%. Comparing base (2e60343) to head (129b067).
Report is 479 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #36102      +/-   ##
==========================================
+ Coverage   80.15%   81.18%   +1.02%     
==========================================
  Files        2179     2246      +67     
  Lines      204875   226889   +22014     
==========================================
+ Hits       164227   184199   +19972     
- Misses      35303    36953    +1650     
- Partials     5345     5737     +392     

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