Target detection not working for ARM_MUSCA_B1

[LDong-Arm]

Describe the bug
mbed-tools detect is not working for ARM_MUSCA_B1. Same with the -f option of mbed-tools compile, so it's a target detection issue.

To Reproduce
Steps to reproduce the behavior:

1. Connect an ARM_MUSCA_B1 board to PC and wait for it to enumerate
2. Run mbed-tools detect. The error is

ERROR: Could not identify a board with the product code: '5007'.
No connected Mbed devices found.

Expected behavior
The target ARM_MUSCA_B1 should be recognised. Output from the old tools (mbed detect):

[mbed] Detected ARM_MUSCA_B1, port /dev/tty.usbmodem143102, mounted /Volumes/MUSCA_B, interface version 0242:
[mbed] Supported toolchains for ARM_MUSCA_B1
| Target       | mbed OS 2 | mbed OS 5 |    ARM    | uARM |  GCC_ARM  | IAR |
|--------------|-----------|-----------|-----------|------|-----------|-----|
| ARM_MUSCA_B1 |     -     | Supported | Supported |  -   | Supported |  -  |
Supported targets: 1
Supported toolchains: 2

Screenshots
If applicable, add screenshots to help explain your problem.

Desktop (please complete the following information):

• OS: macOS
• Version: 11.2.3 (Big Sur)

Mbed (please complete the following information):

• Device: ARM_MUSCA_B1
• Mbed OS Version: 6.9.0
• Mbed CLI 2 Version: 7.10.0

Additional context
Add any other context about the problem here.

[LDong-Arm]

ARM_MUSCA_B1 boards are relatively rare and I have one, so I assigned this issue to myself. It's not critical so I may not fix it right away.

[Patater]

Could this be because targets/targets.json for the B1 doesn't have a "detect_code" entry? S1 has it as 5009. I don't see an entry for B1.

[Patater]

Looks my proposed fix to add detect_code to targets.json isn't going to work if the tools don't look at the detect_code.

[LDong-Arm]

Looks my proposed fix to add detect_code to targets.json isn't going to work if the tools don't look at the detect_code.

Thanks for the PR, it's needed anyway.

[rwalton-arm]

We probably need to update the online database. Looks like we only have an entry for MUSCA_S1.