test: PC-13893 Make acceptance test forward compatible (#312)

## Motivation

`value` field of `objective` for Composite SLO is being
[deprecated](#295).
Before the update in can be made, a N9 platform first needs to be
[updated](nobl9/n9#15406) and new version of SDK
needs to be [released](nobl9/nobl9-go#549). To
be able to release changes in the platform, e2e tests of the latest
released SDK and Terraform Provider need to pass against it.

## Summary

E2E test assertions will pass with and without
[changes](nobl9/n9#15406) in N9 platform.

## Related changes

nobl9/nobl9-go#551
nobl9/nobl9-go#549
nobl9/n9#15406
#312
#295

## Testing

Run `make test/e2e` on both environments containing and not containing
nobl9/n9#15406.

nobl9/resource_slo_test.go

@@ -1027,7 +1027,7 @@ resource "nobl9_slo" ":name" {
    display_name = "obj1"
    name         = "tf-objective-1"
    target       = 0.7
-   value        = 1
+   value        = 0
    composite {
      max_delay = "45m"
      components {
@@ -1089,7 +1089,7 @@ resource "nobl9_slo" ":name" {
    display_name = "obj1"
    name         = "tf-objective-1"
    target       = 0.7
-   value        = 1
+   value        = 0
    time_slice_target = 0.7
    composite {
      max_delay = "45m"