Bug/issue enhanced use latest sprint

[fivetran-catfritz]

Are you a current Fivetran customer?

Fivetran created PR.

What change(s) does this PR introduce?

🚨 Breaking Changes

For model jira__issue_enhanced, updated column names sprint_id and sprint_name to current_sprint_id and current_sprint_name, respectively, to confirm the record is for the current sprint. (#76)

🐞 Bug Fix

Updated logic for model int_jira__issue_sprint to adjust how current sprint is determined. It now uses the newest started_at date of the sprint instead of the updated_at date. (#76)

Did you update the CHANGELOG?

• [x] Yes

Does this PR introduce a breaking change?

• [ ] Yes (please provide breaking change details below.)
• [x] No (please provide an explanation as to how the change is non-breaking below.)

Did you update the dbt_project.yml files with the version upgrade (please leverage standard semantic versioning)? (In both your main project and integration_tests)

• [x] Yes

Is this PR in response to a previously created Bug or Feature Request

• [x] Yes, Issue/Feature #71
• [ ] No

How did you test the PR changes?

• [x] Buildkite
• [x] Local (please provide additional testing details below)

Select which warehouse(s) were used to test the PR

• [x] BigQuery
• [x] Redshift
• [x] Snowflake
• [x] Postgres
• [ ] Databricks
• [ ] Other (provide details below)

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:seedling: **Feedback** We are so excited you decided to contribute to the Fivetran community dbt package! We continue to work to improve the packages and would greatly appreciate your [feedback](https://www.surveymonkey.com/r/DQ7K7WW) on our existing dbt packages or what you'd like to see next.

[fivetran-catfritz]

@fivetran-reneeli I have updated and ready for your review! Thanks!