feat(conf): Add migrations.ttlSecondsAfterFinished to chart template

[ashman1984]

What this PR does / why we need it:

Adds migrations.ttlSecondsAfterFinished as an option in the chart template for allowing removal of migrations containers after a specified time.

The use of ttlSecondsAfterFinished was first discussed here, however the TTL mechanism was in beta at the time.

Special notes for your reviewer:

Checklist

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

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

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All committers have signed the CLA.

[CLAassistant]

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[pmalek]

Thanks for the PR. Generally this looks good.

Since we're adding a possible value to be set in values.yaml can you please add that under

charts/charts/kong/values.yaml

Lines 469 to 470 in 28af4cb

	# Enable/disable migration jobs, and set annotations for them
	migrations:

and in

charts/charts/kong/README.md

Lines 621 to 625 in 28af4cb

	| migrations.preUpgrade | Run "kong migrations up" jobs | `true` |
	| migrations.postUpgrade | Run "kong migrations finish" jobs | `true` |
	| migrations.annotations | Annotations for migration job pods | `{"sidecar.istio.io/inject": "false" |
	| migrations.jobAnnotations | Additional annotations for migration jobs | `{}` |
	| migrations.backoffLimit | Override the system backoffLimit | `{}` |

[pmalek]

Please also make sure to sign the CLA so that the PR can merge.

[pmalek]

Thanks for the contribution @ashman1984 🙇