[falcosidekick-ui] Customize initcontainer Docker image

[nlamirault]

What type of PR is this?

Uncomment one (or more) /kind <> lines:

/kind bug

/kind cleanup

/kind design

/kind documentation

/kind failing-test

/kind feature

If this PR will release a new chart version please make sure to also uncomment the following line:

/kind chart-release

Any specific area of the project related to this PR?

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/area falco-chart

/area falco-exporter-chart

/area falcosidekick-chart

/area event-generator-chart

/area k8s-metacollector

What this PR does / why we need it:

With actual Helm chart it is not possible to change the Docker registry used by the init Container from Falcosidekick UI.

Which issue(s) this PR fixes:

Fixes #

Special notes for your reviewer:

Checklist

• [x] Chart Version bumped
• [x] Variables are documented in the README.md
• [x] CHANGELOG.md updated

[poiana]

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[Issif]

The PR #703 contains your change and more, so I preferred to merge it. Thanks for your help.