fix(rdb): allow updates from bssd to lssd if new node type has enough space

[Mia-Cross]

I noticed a case that did not occur in the tests but there was a bug when changing the volume type from bssd to lssd as the volume_size_in_gb attribute goes from the given value to 0 (the volume size depends on the node type). And since we carry out the upgrades starting from the volume and ending with the node type, that resulted in the API rejecting the update of the volume_type because the node_type should be updated first.

To fix the issue, this PR adds the comparing of the actual and the wanted storage capacities to see if the node_type has to be updated first.

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 51.72414% with 28 lines in your changes are missing coverage. Please review.

Project coverage is 73.03%. Comparing base (46d62b5) to head (b88254f).

Files	Patch %	Lines
scaleway/resource_rdb_instance.go	51.72%	24 Missing and 4 partials ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #2461      +/-   ##
==========================================
+ Coverage   73.01%   73.03%   +0.01%     
==========================================
  Files         242      242              
  Lines       35350    35373      +23     
==========================================
+ Hits        25810    25833      +23     
+ Misses       7316     7313       -3     
- Partials     2224     2227       +3     

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.