e11cdc9  logging: Add log severity level to net.cpp (klementtan)
a829064 logging: Add severity level to logs. (klementtan)

Pull request description:

  **Overview**: This PR introduces a new macro, `LogPrintLevel`, that allows developers to add logs with the severity level. Additionally, it will also print the log category if it is specified.

  Sample log:
  ```
  2022-03-04T16:41:15Z [opencon] [net:debug] trying connection XX.XX.XXX.XXX:YYYYY lastseen=2.7hrs
  ```

  **Motivation**: This feature was suggested in #20576 and I believe that it will bring the following benefits:
  * Allow for easier filtering of logs in `debug.log`
  * Can be extended to allow users to select the minimum level of logs they would like to view (not in the scope of this PR)

  **Details**:
  * New log format. `... [category:level]...`. ie:
    * Do not print category if `category == NONE`
    * Do not print level if `level == NONE`
    * If `category == NONE` and `level == NONE`, do not print any fields (current behaviour)
  * Previous logging functions:
    * `LogPrintf`:  no changes in log as it calls `LogPrintf_` with `category = NONE` and `level = NONE`
    * `LogPrint`: prints additional `[category]` field as it calls `LogPrintf_` with `category = category` and `level = NONE`
  * `net.cpp`: As a proof of concept, updated logs with obvious severity (ie prefixed with `Warning/Error:..`) to use the new logging with severity.

  **Testing**:
  * Compiling and running `bitcoind` with this PR should instantly display logs with the category name (ie `net/tor/...`)
  * Grepping for `net:debug` in `debug.log` should display the updated logs with severity level:
    <details>
    <summary>Code</summary>

    ```
    $ grep "net:debug" debug.log

    2022-03-04T16:41:15Z [opencon] [net:debug] trying connection XXX:YYY lastseen=2.7hrs
    2022-03-04T16:41:16Z [opencon] [net:debug] trying connection XXX:YYY lastseen=16.9hrs
    2022-03-04T16:41:17Z [opencon] [net:debug] trying connection XXX:YYY lastseen=93.2hrs
    2022-03-04T16:41:18Z [opencon] [net:debug] trying connection XXX:YYY lastseen=2.7hrs
    ```
    </details>

ACKs for top commit:
  laanwj:
    Code review and lightly tested ACK e11cdc9

Tree-SHA512: 89a8c86667ccc0688e5acfdbd399aac1f5bec9f978a160e40b0210b0d9b8fdc338479583fc5bd2e2bc785821363f174f578d52136d228e8f638a20abbf0a568f

The LogRatelimiter class implements a fixed window rate limiter. The
rate limiter allows a fixed amount of bytes to be consumed within a
fixed time window.

[log] Introduce source location type

The SourceLocation type stores the filename and line of a source code
location.
In a later commit we use this type as the key type in an unordered map
and set to keep track of rate limters for each location.

[config] Add -ratelimitlogging config option

The -ratelimitlogging can be used to enable/disable the rate limiting to
disk. Rate limiting is enabled by default.

[log] Add two new categories for unconditional logging

We create two new categories `UNCONDITIONAL_ALWAYS` and
`UNCONDITIONAL_RATE_LIMITED` that are always enabled by default.

LogPrintf now logs using the `UNCONDITIONAL_RATE_LIMITED` category which
will start to apply rate limiting in a later commit.

For some log locations it might be safe to allow more frequent logging
without rate limiting. These locations should use the
`UNCONDITIONAL_ALWAYS` category.

[validation] Exempt UpdateTipLog from rate limiting

UpdateTipLog logs everytime a new tip is activated. This occurs at an
increased frequency during IBD and should therefore be exempt from rate
limiting.

[log] Add rate limiting to LogPrintf

To mitigate disk filling attacks caused by unsafe usages of LogPrintf,
we rate limit LogPrintf by using the fixed window rate limiter
(BCLog::LogRatelimiter) introduced in an earlier commit.

The rate limiting logic is applied per source location instead of
globally. A source location is allowed to log up to 1 MiB per hour.
Source locations that violate the limit will have their logs supressed
for up to one hour.

[test util] Mark ~DebugLogHelper as noexcept(false)

We mark ~DebugLogHelper as noexcept(false) to be able to catch the
exception it throws. This lets us use it in test in combination with
BOOST_CHECK_THROW and BOOST_CHECK_NO_THROW to check that certain log
messages are (not) logged.

[test] Check for expected log rate limiting messages

[test] Test for expected file size changes when rate limiting is enabled

[test] Check that log rate limiting is disabled for exempt source locations

[test] Check that rate limiting can be disabled