Fixed the digits verification for seqCol arrays to be digested - ingestion endpoint

[waterflow80]

closes #45
I was able to insert seqCol objects related to asm_accession: GCA_002263795.4 locally.

[waterflow80]

I think this PR might solve the issue for most of the assembly's (including GCA_002263795.4),
however it will fail when having an assembly with an array of names composed only with digits, eg: [100, 101, 102, 103] (Not sure if it does exist)
Because in that case it will be treated like a lengths array in the toString() method of the JSONExtData class.

I will make another PR that solves this issue with all possible test cases where I'll be refactoring the toString() method.

If there are currently some assemblies that has only digits in their names array then I believe we should discard this PR, otherwise we can keep it to make the service work with most of the assemblies and do the refactoring later.