🌱 Fix conversion tests + change RemoteSyncer fields name

[damsien]

This PR fixes:

• The wrong conversion webhook implementation in the envtest.

This PR brings:

• A renaming of 2 fields of the RemoteSyncer object:

1. processMode -> strategy
2. pushMode -> targetStrategy

This PR removes support for v1aplhaX api versions

[codecov]

Codecov Report

Attention: Patch coverage is 20.00000% with 8 lines in your changes missing coverage. Please review.

Files with missing lines	Patch %	Lines
internal/webhook/v1beta3/remotesyncer_webhook.go	0.00%	2 Missing and 3 partials ⚠️
pkg/api/v1beta3/remotesyncer_conversion.go	0.00%	1 Missing ⚠️
pkg/api/v1beta3/remoteuser_conversion.go	0.00%	1 Missing ⚠️
pkg/api/v1beta3/remoteuserbinding_conversion.go	0.00%	1 Missing ⚠️

Files with missing lines	Coverage Δ
internal/interceptor/webhook_request_checker.go	74.90% <100.00%> (ø)
pkg/api/v1beta3/remotesyncer_types.go	100.00% <ø> (ø)
pkg/api/v1beta3/remotesyncer_conversion.go	0.00% <0.00%> (ø)
pkg/api/v1beta3/remoteuser_conversion.go	0.00% <0.00%> (ø)
pkg/api/v1beta3/remoteuserbinding_conversion.go	0.00% <0.00%> (ø)
internal/webhook/v1beta3/remotesyncer_webhook.go	41.09% <0.00%> (ø)

... and 2 files with indirect coverage changes