Add block explorer backend to vegacapsule

[daniel1302]

We have a backend for block explorer. We added it to stagnet3 here: https://github.com/vegaprotocol/networks-internal/pull/120/files

But it would be nice to add support for it in vegacapsule.

Useful commands:

• vega blockexplorer init --home ...
• vega blockexplorer start --home ...

Related PRs:

• feat: first version of block explorer backend vega#6280

[zale144]

This one is a bit of a challenge. I believe the work I did previously to accommodate the bots into capsule (#374) would be adequate for this use case. The idea for that run-custom-binaries PR is to be able to run any binary as long as we provide the config template and correct path and command with args. In the case of BE it's a bit more complicated because we e need to implement a mechanism that would initiate the database prior to starting the BE backend. I'm not entirely sure where that would happen. If not run custom binaries, then probably best hardcode it.