Fixes up admin cluster command for adding search attributes to be indexed

[mastermanu]

Changed the --search_attr_type flag to take in an English readable name (e.g. Keyword, Int, String, etc) instead of an integer (which is less intuitive and should be hidden from the end user anyway).

• Fixes confusion for the user around which integer to map to the type of field they want indexed.
• Removes the need to document the attribute type integer in our temporal docs (which just causes confusion)

• Tested change locally against my developer environment. Verified addition of different types of attributes (int and keyword) and that search worked properly from the command-line.

tctl-only change. No server change here.