Update GitHub issue templates to remove CKAN-era references

[SueValente]

What

Review and update the issue templates in .github/ISSUE_TEMPLATE/ to remove CKAN references and reflect current systems and processes.

Why

These templates are used actively for O+M work. Stale references to CKAN, old tools, or old processes create confusion for the team.

Done When

• o-and-m.md reviewed and updated for current stack
• harvest.md reviewed and updated for H2.0
• onboard-team-member.md reviewed and updated (coordinate with onboarding ticket)
• offboard-team-member.md reviewed and updated (coordinate with offboarding ticket)

Notes

Templates live at https://github.com/GSA/data.gov/blob/main/.github/ISSUE_TEMPLATE/. Changes require a PR against the main data.gov repo. Coordinate with the onboarding/offboarding ticket already in the queue before touching those two templates.