SAR-225 Add `eb` id endpoint to skuid service

• Added the ExecutionBlock eb endpoint.
• Added sample request to doc and a test for it.
• Once merged to master
  • I'll push a new docker image build to nexus
  • I'll build and push a new chart version.

curl http://127.0.0.1:8080/skuid/ska_id/eb
"{\"ska_uid\": \"eb-t0001-20210426-00005\", \"generator_id\": \"t0001\"}"

In [1]: from ska_ser_skuid.client import SkuidClient

In [2]: client = SkuidClient("http://127.0.0.1:8080")

In [3]: client.fetch_skuid('eb')
Out[3]: 'eb-t0001-20210426-00004'

In [4]: