Allow to insert and update with empty value in cli kv

[martinkersner]

Description

This PR adds feature for cli kv. Previously, it was not possible to set value of key-value pair as an empty string. After merging this request, it will be possible.

Fixes #252

When using CLI, you can simply omit the --value parameter. When using insertMany, you can define value as an empty string.

insert

yarn cli kv insert --key [chain] --chain[chain]

update

yarn cli kv update --key [chain] --chain[chain]

insertMany

Example of settings.json file with a key-pair value where value is an empty string.

{
  "EMPTY_FIELD": ""
}

yarn cli kv insertMany --file-path [file-path] --chain [chain]

Type of change

• New feature (non-breaking change which adds functionality)
• This change requires a documentation update

Checklist before requesting a review

• I have performed a self-review of my code.
• If it is a core feature, I have added thorough tests.