Added ability to specify multiple services top be opened with the --console flag

[meyerjrr]

What changed?

Altered the services flag to now be a string slice flag which accepts multiple services (ie assume -c -s s3 -s rds) Which will then open up the console with two tabs one for each of the services.

To do this I altered the logic for creating URLs to now create a list of URL's even when just creating one.

It then loops through all urls created and runs the same browser logic previously used.

Why?

I've been learning vim and have been looking for simple tasks to complete on Granted :D
For #807

How did you test it?

Manually testing assume -c with and without the -s flag for one and multiple services

Running related commands like assume --url assume granted console to confirm no regressions made

Potential risks

string -> stringSlice flag should have no usage changes but all code paths using .String() need to have been changed to ensure correct logic

Altering logic in the assume command has the potential to create regressions in some of the flags logic.

It might be worth noting here that the assume.go file is becoming quite complicated due to small additions over time and could use with a refactor to simplify it down. This would be a big task but could be useful to minimise any regressions being added.

Is patch release candidate?

Link to relevant docs PRs