Enable overriding proxy buffer values

[supreethrao]

• The default proxy buffer size has been changed to 16k
• The default proxy buffer blocks has been changed to 4 16k
• Both of the above values can be overridden with the relevant annotations
• There is a max permissible value and if the annotated value exceeds that, it will be reset to the max permissible value for both of the above fields.

[supreethrao]

Thanks @peterbale