To expose context flags through diagnostic endpoint
`/debug/metrics/flags`.
The current `/debug/metrics/cmdline` only provides the command run by
user. In the case when user runs Erigon using config file, `cmdline`’s
info does not truly reflect the ‘launch setting' and flags set that
Erigon is running on.
## Example
### Command
```
erigon --datadir /tmp/data --config test.yaml
```
### Pseudo config file (in yaml)
```
datadir : '/tmp/data'
chain : "sepolia"
http : true
metrics: true
private.api.addr : "localhost:9090"
http.api : ["eth","debug","net"]
```
### Output
```
SUCCESS
chain=sepolia
config=test.yaml
datadir=/tmp/data
http=true
http.api=eth,debug,net
metrics=true
private.api.addr=localhost:9090
```
