feat(migrations): affinity configuration support

[psmolkin]

What this PR does / why we need it:

Add pod affinity configuration to the migration jobs templates.

Which issue this PR fixes

The current Kong chart implementation already supports pod affinity configuration for deployment/daemonset. So far this has not been reflected in the migration jobs templates. However, this may be necessary in case, for example, not all availability zones provide k8s nodes with network access to the database.

• add affinity section to pod spec in the migrations templates

Special notes for your reviewer:

Checklist

[Place an '[x]' (no spaces) in all applicable fields. Please remove unrelated fields.]

• [x] PR is based off the current tip of the main branch.
• [x] Changes are documented under the "Unreleased" header in CHANGELOG.md
• [x] New or modified sections of values.yaml are documented in the README.md
• [x] Commits follow the Kong commit message guidelines

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