Fix:(issue_2056) Add cmd.XXXArgs() functions for retrieving args

[dearchap]

What type of PR is this?

(REQUIRED)

• feature

What this PR does / why we need it:

(REQUIRED)

Add functions to allow Args access. Two classes of functions are available on the command
one for single value arguments and one for multi value/slice

Which issue(s) this PR fixes:

(REQUIRED)

Fixes #2056

Special notes for your reviewer:

(fill-in or delete this section)

Testing

(fill-in or delete this section)

go test -run=Test*Args

Release Notes

(REQUIRED)

New classes of accessor functions for different argument types has been added. One for single value arguments and one for multiple values/slices

- StringArg
- StringArgs
- FloatArg
- FloatArgs
- IntArg
- IntArgs
- UintArg
- UintArgs
- TimestampArg
- TimestampArgs

Only the single value arguments can have a default value. Parsing of arguments will stop at the first argument that fails either parsing or constraint mismatch

[meatballhat]

I fully admit that I mostly skimmed this! I'd love to know the answer to @Juneezee's question, too, but I don't have any blocking feedback.

Other notes:

• I'm reminded that I'd like to make sure argument and flag types from external packages are possible.
• The use of private members in the public ArgumentBase declarations still looks funny to me 🤔 e.g. the timestampValue in ArgumentsBase[time.Time, TimestampConfig, timestampValue]