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GH-44934: [Dev] Remove JIRA remnants (#44936)

### Rationale for this change

We are not using JIRA anymore in the project

### What changes are included in this PR?

Remove JIRA from:
- documentation
- pr and issue templates
- comment bot
- merge script

### Are these changes tested?

Via CI

### Are there any user-facing changes?

No
* GitHub Issue: #44934

Lead-authored-by: Raúl Cumplido <raulcumplido@gmail.com>
Co-authored-by: Jacob Wujciak-Jens <jacob@wujciak.de>
Co-authored-by: Sutou Kouhei <kou@cozmixng.org>
Signed-off-by: Jacob Wujciak-Jens <jacob@wujciak.de>