Add delete strategy to reloader

[armandgrillet]

What type of PR is this?
Bug

What this PR does/ why we need it:
Trying to fix issue when upgrading KBA: https://mesosphere.slack.com/archives/CLETZF5U6/p1615265348020900

Which issue(s) this PR fixes:

Special notes for your reviewer:

Does this PR introduce a user-facing change?:

When upgrading from a release that used helm 2 to install, reloader cannot be cleanly upgraded due to selector changes. This adds a flag that causes reloader to be uninstalled before being upgraded. This should have no effect on running applications.

Checklist

• The commit message explains the changes and why are needed.
• The code builds and passes lint/style checks locally.
• The relevant subset of integration tests pass locally.
• The core changes are covered by tests.
• The documentation is updated where needed.

[d2iq-mergebot]

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@mesosphere-mergebot backport  

[joejulian]

Rebasing this against master then I'll use the bot to backport.

[joejulian]

@mesosphere-mergebot backport release/3 release/3.3

[d2iq-mergebot]

Backport PR for release/3: #957
Conflicts present in files:

addons/reloader/reloader.yaml

Backport PR for release/3.3: #958
Conflicts present in files:

addons/reloader/reloader.yaml