Case-insensitive tab completions

[kangasta]

Follow-up for #102.

Case-insensitive argument matching was implemented in #335. Add similar functionality for tab completions as well.

[sharanrajt]

Hi @kangasta, Can I work on this?

[kangasta]

Yes, no blockers, but note that I'm not sure how well this is supported by by shells or the CLI library we use (cobra), so first step would be verify if this is possible. If there is no clean solution, let's document the findings and close this.

[sharanrajt]

From my investigation, This codebase has the infrastructure for case-insensitivity in internal/completion/helpers.go. The caseSensitive parameter controls that behavior.

But all the completion providers are calling it with true, for eg: internal/completion/account.go

MatchStringPrefix(vals, toComplete, true)  // Case-sensitive

which can we replaced with

MatchStringPrefix(vals, toComplete, false)  // Case-insensitive

If current auto completion is working as expected for case-sensitive cases then just the above hack should work fine with few more unit tests added.