[Telephony] SerialNumberInput should support multi-lang and custom user-provided substitutions

[stevengum]

Is your feature request related to a problem? Please describe.

The SerialNumberInput node in latest (41e71b7) only supports a very small amount of substitutions for only English.

Substitutions (or disambiguating user input) become relevant when Speech-to-Text is involved with a chatbot (e.g., the Telephony channel). A user might say the letter "A", but STT might record it as the number "8", which would result in the user proceeding down an unhappy path. This issue applies for other languages as well, which means the lack of multi-language support can be a blocker for certain teams using the node.

Describe the solution you'd like

• Composer users should be able to provide the substitutions tables for languages
• Code-first users should be able to provide substitutions tables for languages

One potential approach for Composer users would be to have a configurable path with filenames in an expected format, e.g. substitution-en.json, substitution-es.json to provide their own substitution tables. Note the language code after the substitution- prefix. (example substitution-en.json in private repository).

So in the Composer UI, a user might provide the filepath as an input when configuring the node with the substitution files for more granular control. An alternative that has less repetitive configuration would be configuring a bot-level filepath where substitution tables would be found, so that all nodes with substitution support automatically use the tables.

Additional context

Latest PR, that udpated the functionality of the SerialNumberInput node