Sizing Calculator: added unit tests and minor restructuring

[shaharuk-yb]

Associated with JIRA tasks:

• https://yugabyte.atlassian.net/browse/DB-11648
• https://yugabyte.atlassian.net/browse/DB-11696
  Includes following changes:
• Added unit tests to the sizing calculator
• restructured some code in sizing.go to support isolated run of the unit tests
• added github actions workflow to run unit tests

Function Under Test	Test name	Test scenario
getSourceMetadata	TestGetSourceMetadata_SuccessReadingSourceMetadata	successfully able to connect and load the source metadata
getSourceMetadata	TestGetSourceMetadata_QueryErrorIfTableDoesNotExistOrColumnsUnavailable	if table_index_stat does not exist in the assessment.db or one of the required column does not exist in the table
getSourceMetadata	TestGetSourceMetadata_RowScanError	verify if the all columns datatypes are correct. Expecting failure in case of unsupported data type. Example: expected column value is int but in assessment.db, float value is provided. Hence, it will fail to read/typecast
getSourceMetadata	TestGetSourceMetadata_NoRows	verify if there are no rows in the source metadata
shardingBasedOnTableSizeAndCount	TestShardingBasedOnTableSizeAndCount_TableWithSizePlacedInColocated	validate if the source table of size in colocated limit is correctly placed in colocated table recommendation
shardingBasedOnTableSizeAndCount	TestShardingBasedOnTableSizeAndCount_WithIndexes_ColocateAll	validate if the source table and index of size in colocated limit is correctly placed in colocated table recommendation
shardingBasedOnTableSizeAndCount	TestShardingBasedOnTableSizeAndCount_ColocatedLimitExceededBySize	validate if the source table and index of size in colocated limit exceeds the size limit and respective tables need to be put in sharded
shardingBasedOnTableSizeAndCount	TestShardingBasedOnTableSizeAndCount_ColocatedLimitExceededByCount	validate if the source table and index of size in colocated limit exceeds limit of maximum supported num objects and respective tables need to be put in sharded
shardingBasedOnTableSizeAndCount	TestShardingBasedOnTableSizeAndCount_NoColocatedTables	validate if the tables of size more than max colocated size supported are put in the sharded tables
shardingBasedOnOperations	TestShardingBasedOnOperations_CanSupportOpsRequirement	validate that the tables should be removed from colocated and added to sharded as the ops requirement is high
shardingBasedOnOperations	TestShardingBasedOnOperations_CannotSupportOpsAndNeedsSharding	validate that the tables should be removed from colocated and added to sharded as the ops requirement is higher than supported
checkShardedTableLimit	TestCheckShardedTableLimit_WithinLimit	validate that the sharded table limits is not exceeded and failure reasoning should be empty
checkShardedTableLimit	TestCheckShardedTableLimit_LimitExceeded	validate that the sharded table limits is exceeded and failure reasoning is generated as expected
findNumNodesNeededBasedOnThroughputRequirement	TestFindNumNodesNeededBasedOnThroughputRequirement_CanSupportOps	validate that the throughput requirements are supported and no scaling is needed
findNumNodesNeededBasedOnThroughputRequirement	TestFindNumNodesNeededBasedOnThroughputRequirement_NeedMoreNodes	validate that the throughput requirements cannot be supported by existing nodes and scaling is needed
findNumNodesNeededBasedOnTabletsRequired	TestFindNumNodesNeededBasedOnTabletsRequired_CanSupportTablets	validate that the tablets requirements are supported and no scaling is needed
findNumNodesNeededBasedOnTabletsRequired	TestFindNumNodesNeededBasedOnTabletsRequired_NeedMoreNodes	validate that the tablets cannot be supported by existing nodes and scaling is needed
pickBestRecommendation	TestPickBestRecommendation_PickOneWithOptimalNodesAndCores	validate if the recommendation with optimal nodes and cores is picked up
pickBestRecommendation	TestPickBestRecommendation_PickOneWithOptimalNodesAndCoresWhenSomeHasFailures	validate if the recommendation with optimal nodes is picked up when some of the recommendation has failure reasoning
pickBestRecommendation	TestPickBestRecommendation_PickLastMaxCoreRecommendationWhenNoneCanSupport	validate if the recommendation with optimal nodes and cores is picked up for showing failure reasoning
calculateTimeTakenAndParallelJobsForImport	TestCalculateTimeTakenAndParallelJobsForImport_ValidateFormulaToCalculateImportTime	validate the formula to calculate the import time
getReasoning	TestGetReasoning_NoObjects	validate reasoning when there are no objects(empty colocated and sharded objects)
getReasoning	TestGetReasoning_OnlyColocatedObjects	validate reasoning when there are only colocated objects
getReasoning	TestGetReasoning_OnlyShardedObjects	validate reasoning when there are only sharded objects
getReasoning	TestGetReasoning_ColocatedAndShardedObjects	validate reasoning when there are colocated and sharded objects
getReasoning	TestGetReasoning_Indexes	validate reasoning when there are colocated and sharded objects with indexes

[makalaaneesh]

Thanks for this @shaharuk-yb , this is very thorough!!
Did not go through all the logic in detail, as you would be the better judge, but the overall structure looks good.

Just had one comment, pls look into that before merging