Update missing conversion of OktaAccountName

[xarses]

GetSAMLLoginURL was using hard-coded "okta-creds" instead of the lookup
for OktaAccountName, in cases where multiple accounts are used, this can
result in building an incorrect login URL

[nickatsegment]

This will mean existing users will have to readd their creds though I believe?

Just trying to figure out which behaviour is less broken :)

[xarses]

@nickatsegment no I didn't have to add either credential. I was able to recompile the binary and continue with my accounts as is.

Some more clarity on the problem I found was explicitly with aws-okta login other-account where one account was "default" i.e. no explicit account while other-account is explicitly another account. this results in login building a SAMLLoginURL that points to the default instance. This for some reason I haven't bothered to untangle does not happen if its a AssumeRole IAM just if its the SAMLAssumeRole landing account.

Other commands worked as expected without this modification i.e. aws sts get-caller-identity works with and without this change

[nickatsegment]

Cool, I'm convinced