Jira Integration: Allow configuring issue update via parameter

[holger-waschke]

This change allows disabling the update of issue descriptions.

It´s a non breaking change the default is still to update everything. Only if you set the parameter disable_update_description explicit to true the description won´t get updated anymore.

We need this feature as there a lot of jira automations which updates the description itself, jiralert would revert the changes back to the original templated description state once the repeat_interval kicks in and the alert is still active, so it´s handy to have the possibility to disable it.

I added a new unit test for this function to test.

Exempel config

receivers:
- name: jira_alarm
  jira_configs:
  - project: MON
    issue_type: Bug
    resolve_transition: "Geschlossen"
    reopen_transition: "Erfasst"
    reopen_duration: "1h"
    disable_update_description: true