additional activation get features

[rabbah]

Expected Behaviour

These wsk flags are not available on > aio runtime:activation get --help.

> wsk activation get -h
get activation
Usage:
  wsk activation get (ACTIVATION_ID | --last) [FIELD_FILTER] [flags]

Flags:
  -l, --last      retrieves the last activation
  -g, --logs      emit only the logs, stripped of time stamps and stream identifier
  -s, --summary   summarize activation details

The ability to get the last activation or just its logs is quite handy.

Actual Behaviour

> aio runtime:activation get --last
 ›   Error: failed to retrieve the activation: GET https://.../api/v1/namespaces/_/activations/--last Returned 
 ›   HTTP 400 (Bad Request) --> "Activation id length is 6 but must be 32."

The flag --last is being treated as an activation name.

Reproduce Scenario (including but not limited to)

Steps to Reproduce

Platform and Version

> aio version
@adobe/aio-cli/2.1.1 darwin-x64 node-v10.16.3

Sample Code that illustrates the problem

Logs taken while reproducing problem

[rabbah]

I see that last should at least be available per https://github.com/adobe/aio-cli-plugin-runtime/blob/4176e101e5d51c6b2a1da559f32ab9316373c3ef/src/commands/runtime/activation/get.js#L21

[rabbah]

Opened corresponding issue and PR in the appropriate repo for this change.