change the type of volume extend_param to map

[Jason-Zhang9309]

What this PR does / why we need it:

change the type of volume extend_param to map
In the API docs the type of root_volume and data_volumes in cce node is Map, but it was String in our code, this problem need to be fixed.

Which issue this PR fixes:
(optional, in fixes #<issue number>(, fixes #<issue_number>, ...) format, will close that issue when PR gets merged)
fixes #xxx

Special notes for your reviewer:

Release note:

PR Checklist

• Tests added/passed.
• Documentation updated.
• Schema updated.

Acceptance Steps Performed

make testacc TEST='./huaweicloud' TESTARGS='-run TestAccCCENodeV3_basic'
==> Checking that code complies with gofmt requirements...
TF_ACC=1 go test ./huaweicloud -v -run TestAccCCENodeV3_basic -timeout 360m -parallel 4
=== RUN   TestAccCCENodeV3_basic
=== PAUSE TestAccCCENodeV3_basic
=== CONT  TestAccCCENodeV3_basic
--- PASS: TestAccCCENodeV3_basic (1698.66s)
PASS
ok      github.com/huaweicloud/terraform-provider-huaweicloud/huaweicloud       1698.739s