Remove unused probot automations; Update GitOps config for stale issues.

[sjwaight]

This PR does the following:

• Remove the old probot-driven configs for automation of issue management to avoid confusion around what's driving issue management.
• Update GitOps config to better explain what each item does.
• Merge in support for the changes from @chasewilson's PR for networking at cilium (Adds assignees to issues labeled networking and cilium #4571)
• Merge in support for the change from @aritraghosh's PR (Add enhancement to list of excluded labels #4430)
• Merge in support for filters for stale issues from @AllenWen-at-Azure's PR for workflow fixes (Improve the bot in terms of labeling stale issue and closing issue etc. #4514) - note I left out the SLA label change as it was unclear to me the value add.
• Update stale issue management so that issues that have the following criteria are not marked as stale:
  • Assigned to someone
  • Have one of the following labels: stale, feature-request, bug, enhancement, announcement, under-investigation

Known issue: GitOps does not currently provide support for filtering on issues included in GitHub Projects so it's not possible to filter items for staleness based on their inclusion in a project.

[AllenWen-at-Azure]

LGTM

[AllenWen-at-Azure]

@palma21 could you please review and merge this PR? It can help resolve bugs like #4464

[sjwaight]

Superseded by #4728.