Shapshots list admin endpoint

[bluesign]

Closes #228

Description

I was thinking 2 endpoints:

GET /snapshots to list all snapshots, in any case we should add, I guess, it seems pretty nice to have.
GET /snapshots/{snapshotID} Retrieve existing one is also not a problem. ( also 404 on fail )

But it will not be backwards compatible. But if we decide like that ( and move create to POST verb ) I can update the PR

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For contributor use:

• Targeted PR against master branch
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• Code follows the standards mentioned here
• Updated relevant documentation
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[codecov-commenter]

Codecov Report

Merging #241 (59f41eb) into master (dddefb8) will increase coverage by 1.17%.
The diff coverage is 7.69%.

@@            Coverage Diff             @@
##           master     #241      +/-   ##
==========================================
+ Coverage   50.96%   52.14%   +1.17%     
==========================================
  Files          29       26       -3     
  Lines        2372     2054     -318     
==========================================
- Hits         1209     1071     -138     
+ Misses       1019      857     -162     
+ Partials      144      126      -18     

Flag	Coverage Δ
unittests	52.14% <7.69%> (+1.17%)	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
server/emulator.go	12.04% <7.69%> (-0.81%)	⬇️
server/storage.go	41.02% <0.00%> (-8.98%)	⬇️
server/server.go	48.50% <0.00%> (-0.74%)	⬇️
blocks.go	60.00% <0.00%> (ø)
headers.go	21.42% <0.00%> (ø)
storage/badger/store.go
storage/badger/encoding.go
storage/badger/changelog.go
storage/badger/keys.go
storage/badger/config.go
... and 3 more

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[devbugging]

I would say that if we are doing changes in API I would make the API to be more RESTful:
GET /snapshots list all
POST /snapshots create a new snapshot, and provide a name in body
PUT /snapshots/{id} restore a specific snapshot

[devbugging]

@bluesign is this complete and ready for review? sorry I guess we missed it.

[bluesign]

Yeah should be ready, Sorry I forgot this too

[devbugging]

@bluesign left a couple of questions, the biggest one is a check whether the store is of type badger, and also generally to think how will this work with the store refactor that happened meanwhile.

[bluesign]

@sideninja this one also I will handle Monday if not urgent

[devbugging]

@bluesign are we ok to merge?

[bluesign]

@bluesign are we ok to merge?

sorry I missed this, this can be merged.

[devbugging]

Could we add this to the CLI as a command 🙏

[bluesign]

@sideninja very good idea, I will make a PR