Instrument the aws-sdk-lambda gem and upon function invocations
performed by the client, create external request segments that include
AWS resource information.

there are 2 routes errors can take:

* exceptions thrown from the client SDK
  * used for HTTP 4xx/5xx responses
  * use for the client SDK itself raising an internal error
* an unhandled function error which sets the `:function_error` key in
  the response

require Ruby 2.5+ for testing aws-sdk-lambda

update to match dev changes regarding AWS account id

The function invocation methods offered by the aws-sdk-lambda gem take
the `:function_name` argument in the form of `<function name>:<alias>`
or `<function name>:<version>` when an alias or version is involved. The
agent will simply preserve the extra info and the colon delimiter and
segment naming and AWS arn creation will simply end up doing the right
thing with the extra alias or version info.

update CHANGELOG.md for aws-sdk-lambda

don't attempt to determine the region twice within a single method and
simply re-use the result of the single call

remove large source code comment that exists in the instrumentation
generator as boilerplate for the new instrumentation author to review
and remove

use separate error handling for errors raised by the gem itself and
errors raised by the agent.

Errors raised by the gem need to be noticed by the agent (sent to New
Relic) and re-raised to the user's app.

Errors raised by the agent need to be logged but not impact the
returning of the successful gem invocation response.

Co-authored-by: Kayla Reopelle <87386821+kaylareopelle@users.noreply.github.com>