Improvement to JIRA integration

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Description

The JIRA integration is nice, but is lacking on two fronts.

• It creates a comment and a link in JIRA. The comment is adding email noise.

• When a branch is merged into another one, another link to the same commit is added to the JIRA issue.

Proposal

• It should have an option to only create a link in JIRA, and not adding the comment.

• It should check if a link to the same commit hash exists in JIRA, if so, the link should not be added again.