feat: Allow controlling sidecar environment variables

[gnosek]

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

Any specific area of the project related to this PR?

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/area build

/area tests

/area proposals

What this PR does / why we need it:

Without this PR, the injected sidecars are pretty much forced to run with the default environment. This PR introduces two ways to control the sidecar environment:

1. Any changes to the environment in the top-level environment_variables section are propagated to sidecars
2. Each sidecar (mount section in the config) can have its own private environment variables that take preference over the top-level ones

Which issue(s) this PR fixes:

Fixes #

Special notes for your reviewer:

[poiana]

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[gnosek]

The tests fail because they use the released kilt version in cfn_patcher, but we do need an upgraded one (from this PR).

Do we want something like this?

diff --git a/runtimes/cloudformation/go.mod b/runtimes/cloudformation/go.mod
index 87c5840..d96f33f 100644
--- a/runtimes/cloudformation/go.mod
+++ b/runtimes/cloudformation/go.mod
@@ -42,3 +42,5 @@ require (
        golang.org/x/sys v0.9.0 // indirect
        gopkg.in/yaml.v3 v3.0.1 // indirect
 )
+
+replace github.com/falcosecurity/kilt/pkg => ../../pkg