Add support for 99.73 confidence interval [AP-3002] (#1449)

# Description

Extend `MSG_POS_LLH_ACC` message so `confidence_and_geoid` flags support
99.73 confidence interval

# API compatibility

no API compatibility risk: the added support for confidence interval
99.73 fits within existing bits allocated for confidence flags

## API compatibility plan

n/a

# JIRA Reference

https://swift-nav.atlassian.net/browse/AP-3002

---------

Co-authored-by: Ivan Smolyakov <[email protected]>

Author: ismolyakov

c/include/libsbp/navigation_macros.h

@@ -434,6 +434,7 @@
 #define SBP_POS_LLH_ACC_CONFIDENCE_LEVEL_3935 (1)
 #define SBP_POS_LLH_ACC_CONFIDENCE_LEVEL_6827 (2)
 #define SBP_POS_LLH_ACC_CONFIDENCE_LEVEL_9545 (3)
+#define SBP_POS_LLH_ACC_CONFIDENCE_LEVEL_9973 (4)
 #define SBP_POS_LLH_ACC_TYPE_OF_REPORTED_TOW_MASK (0x1u)
 #define SBP_POS_LLH_ACC_TYPE_OF_REPORTED_TOW_SHIFT (5u)
 #define SBP_POS_LLH_ACC_TYPE_OF_REPORTED_TOW_GET(flags)               \

docs/sbp.pdf

@@ -4724,6 +4724,9 @@ pub mod msg_pos_llh_acc {
 
         /// 95.45%
         _9545 = 3,
+
+        /// 99.73%
+        _9973 = 4,
     }
 
     impl std::fmt::Display for ConfidenceLevel {
@@ -4732,6 +4735,7 @@ pub mod msg_pos_llh_acc {
                 ConfidenceLevel::_3935 => f.write_str("39.35%"),
                 ConfidenceLevel::_6827 => f.write_str("68.27%"),
                 ConfidenceLevel::_9545 => f.write_str("95.45%"),
+                ConfidenceLevel::_9973 => f.write_str("99.73%"),
             }
         }
     }
@@ -4743,6 +4747,7 @@ pub mod msg_pos_llh_acc {
                 1 => Ok(ConfidenceLevel::_3935),
                 2 => Ok(ConfidenceLevel::_6827),
                 3 => Ok(ConfidenceLevel::_9545),
+                4 => Ok(ConfidenceLevel::_9973),
                 i => Err(i),
             }
         }

rust/sbp/src/messages/navigation.rs

@@ -743,6 +743,7 @@ definitions:
                                   - 1: 39.35%
                                   - 2: 68.27%
                                   - 3: 95.45%
+                                  - 4: 99.73%
               - n_sats:
                     type: u8
                     desc: Number of satellites used in solution.