Add /header RPC endpoint

[hu55a1n1]

Implements the /header RPC endpoint (#832).

• Referenced an issue explaining the need for the change
• Updated all relevant documentation in docs
• Updated all code comments where relevant
• Wrote tests
• Added entry in .changelog/

[codecov-commenter]

Codecov Report

Merging #1101 (2af6ba6) into v0.23.x (2354801) will decrease coverage by 0.0%.
The diff coverage is 13.3%.

@@            Coverage Diff            @@
##           v0.23.x   #1101     +/-   ##
=========================================
- Coverage     67.3%   67.3%   -0.1%     
=========================================
  Files          212     213      +1     
  Lines        20201   20217     +16     
=========================================
+ Hits         13614   13616      +2     
- Misses        6587    6601     +14     

Impacted Files	Coverage Δ
light-client/src/light_client.rs	71.7% <ø> (ø)
light-client/src/peer_list.rs	88.5% <ø> (ø)
p2p/src/error.rs	0.0% <ø> (ø)
rpc/src/client.rs	5.0% <0.0%> (-0.2%)	⬇️
rpc/src/client/bin/main.rs	0.3% <0.0%> (-0.1%)	⬇️
rpc/src/endpoint/header.rs	0.0% <0.0%> (ø)
tools/rpc-probe/src/common.rs	0.0% <0.0%> (ø)
rpc/src/method.rs	24.7% <50.0%> (+0.9%)	⬆️
config/src/config.rs	55.0% <100.0%> (ø)
tendermint/src/abci/transaction.rs	54.4% <100.0%> (ø)
... and 10 more

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[hu55a1n1]

Seems like the /header endpoint was only added to tendermint 0.35. Will it be backported to 0.34?

[romac]

@mzabaluev This was subsumed by #1193, right? If so, then let's close this

[mzabaluev]

Yes, it's supplanted by #1193.