lightningd: add force-feerates option.

Useful for regtest and testnet.  Sure, you shouldn't use this on mainnet,
but I haven't restricted it because our users are usually pretty clever.

Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>
Fixes: #1806
Changelog-Added: config: `force_feerates` option to allow overriding feerate estimates (mainly for regtest).

doc/lightning-listconfigs.7

@@ -148,6 +148,8 @@ On success, an object is returned, containing:
 .IP \[bu]
 \fBlog-timestamps\fR (boolean, optional): \fBlog-timestamps\fR field from config or cmdline, or default
 .IP \[bu]
+\fBforce-feerates\fR (string, optional): \fBforce-feerates\fR field from config or cmdline, if any
+.IP \[bu]
 \fBsubdaemon\fR (string, optional): \fBsubdaemon\fR fields from config or cmdline if any (can be more than one)
 .IP \[bu]
 \fBtor-service-password\fR (string, optional): \fBtor-service-password\fR field from config or cmdline, if any
@@ -268,4 +270,4 @@ Vincenzo Palazzo \fI<vincenzo.palazzo@protonmail.com\fR> wrote the initial versi
 
 Main web site: \fIhttps://github.com/ElementsProject/lightning\fR
 
-\" SHA256STAMP:f813a777c6e074907980797dafd798a48633469a59e1ac526e2581e2b1a14c83
+\" SHA256STAMP:4591f6c754162b2dcdf82a36d584a48795752d39a986bc1d39c49e0cdbea440f

doc/lightning-listconfigs.7.md

@@ -84,6 +84,7 @@ On success, an object is returned, containing:
 - **log-prefix** (string, optional): `log-prefix` field from config or cmdline, or default
 - **log-file** (string, optional): `log-file` field from config or cmdline, or default
 - **log-timestamps** (boolean, optional): `log-timestamps` field from config or cmdline, or default
+- **force-feerates** (string, optional): `force-feerates` field from config or cmdline, if any
 - **subdaemon** (string, optional): `subdaemon` fields from config or cmdline if any (can be more than one)
 - **tor-service-password** (string, optional): `tor-service-password` field from config or cmdline, if any
 [comment]: # (GENERATE-FROM-SCHEMA-END)
@@ -203,4 +204,4 @@ RESOURCES
 ---------
 
 Main web site: <https://github.com/ElementsProject/lightning>
-[comment]: # ( SHA256STAMP:3c3f2cd354ef5b33ad34febd29b04b1861c62d545c6a5b9181eb2b2b3880258f)
+[comment]: # ( SHA256STAMP:ad98179a7b6254a936d4fde179918b6a975e186adcbc396917a0c2ed2888519e)

doc/lightningd-config.5

@@ -316,6 +316,21 @@ How long to wait before sending commitment messages to the peer: in
 theory increasing this would reduce load, but your node would have to be
 extremely busy node for you to even notice\.
 
+
+ \fBforce-feerates\fR==\fIVALUES\fR
+Networks like regtest and testnet have unreliable fee estimates: we
+usually treat them as the minumum (253 sats/kw) if we can't get them\.
+This allows override of one or more of our standard feerates (see
+\fBlightning-feerates\fR(7))\.  Up to 5 values, separated by '/' can be
+provided: if fewer are provided, then the final value is used for the
+remainder\.  The values are in per-kw (roughly 1/4 of bitcoind's per-kb
+values), an in order are "opening", "mutual_close",
+"unilateral_close", "delayed_to_us", "htlc_resolution", and "penalty"\.
+
+
+You would usually put this option in the per-chain config file, to avoid
+setting it on Bitcoin mainnet!  e\.g\. \fB~rusty/.lightning/regtest/config\fR\.
+
 .SH Lightning channel and HTLC options
 
  \fBlarge-channels\fR
@@ -635,4 +650,4 @@ Main web site: \fIhttps://github.com/ElementsProject/lightning\fR
 Note: the modules in the ccan/ directory have their own licenses, but
 the rest of the code is covered by the BSD-style MIT license\.
 
-\" SHA256STAMP:40c9f5e9e4ee5257e25a1fc196d2c85c3bc5b21d3f390a4e7fafa031c4e7ad5e
+\" SHA256STAMP:d456e1acd004f9528d8772231afdecff1aaa01d80161c833483f6f078f4c7d70

doc/lightningd-config.5.md

@@ -257,6 +257,19 @@ How long to wait before sending commitment messages to the peer: in
 theory increasing this would reduce load, but your node would have to be
 extremely busy node for you to even notice.
 
+ **force-feerates**==*VALUES*
+Networks like regtest and testnet have unreliable fee estimates: we
+usually treat them as the minumum (253 sats/kw) if we can't get them.
+This allows override of one or more of our standard feerates (see
+lightning-feerates(7)).  Up to 5 values, separated by '/' can be
+provided: if fewer are provided, then the final value is used for the
+remainder.  The values are in per-kw (roughly 1/4 of bitcoind's per-kb
+values), an in order are "opening", "mutual_close",
+"unilateral_close", "delayed_to_us", "htlc_resolution", and "penalty".
+
+You would usually put this option in the per-chain config file, to avoid
+setting it on Bitcoin mainnet!  e.g. `~rusty/.lightning/regtest/config`.
+
 ### Lightning channel and HTLC options
 
  **large-channels**

doc/schemas/listconfigs.schema.json

@@ -235,6 +235,10 @@
 	    "type": "boolean",
 	    "description": "`log-timestamps` field from config or cmdline, or default"
 	},
+	"force-feerates": {
+	    "type": "string",
+	    "description": "force-feerate configuration setting, if any"
+	},
 	"subdaemon": {
 	    "type": "string",
 	    "description": "`subdaemon` fields from config or cmdline if any (can be more than one)"