Improve getEvents documentation surrounding filters

[Shaptic]

Closes #2077.

This clarifies the format of a topic filter and introduces an example using the new ** topic syntax. Even though the filters were already defined, they weren't being rendered in the generated docs. Unfortunately another suggestion isn't possible:

Also, change the array[array] to be more descriptive, something like array[array[SegmentMatcher]].

Because types must be OpenRPC primitive types.

[stellar-jenkins]

Preview is available here:
http://developers-pr2084.previews.kube001.services.stellar-ops.com

[stellar-jenkins]

Preview is available here:
http://developers-pr2084.previews.kube001.services.stellar-ops.com

[leighmcculloch]

Thanks for taking this. One ask and one question.

[stellar-jenkins]

Preview is available here:
http://developers-pr2084.previews.kube001.services.stellar-ops.com

[stellar-jenkins]

Preview is available here:
http://developers-pr2084.previews.kube001.services.stellar-ops.com

[stellar-jenkins]

Preview is available here:
http://developers-pr2084.previews.kube001.services.stellar-ops.com

[urvisavla]

Even though the filters were already defined, they weren't being rendered in the generated docs.

I previously highlighted this exact issue when working on the getevents documentation but it wasn't addressed at the time.