ESP32 partition schema and apps support

[bettio]

The following partitioning schema is used and supported:

# Name,   Type, SubType, Offset,  Size, Flags
# Note: if you change the phy_init or app partition offset, make sure to change the offset in Kconfig.projbuild
nvs,      data, nvs,       0x9000,     0x6000,
phy_init, data, phy,       0xf000,     0x1000,
factory,  app,  factory,  0x10000,   0x1C0000,
lib.avm,  data, phy,     0x1D0000,    0x40000,
main.avm, data, phy,     0x210000,   0x100000

The schema should be evolved in order to support more advanced scenarios, such as application updates, and etc...

The following boot sequence should be supported:

1. boot into kernel application
2. decided whether boot app1 or app2
3. open the partition and run the StartupModule:start()

The kernel application might be packed together with the rest of the libraries in order to reduce the partition count, however at the moment booting into lib.avm is not supported.

Also the simplest possible scenario should be supported anyway (that is libraries and just one app packed together).

So the following changes are proposed:

When there is a kernel.avm partition, the kernel.avm partition is always booted.

# Name,   Type, SubType, Offset,  Size, Flags
# Note: if you change the phy_init or app partition offset, make sure to change the offset in Kconfig.projbuild
nvs,      data, nvs,       0x9000,     0x6000,
phy_init, data, phy,       0xf000,     0x1000,
factory,  app,  factory,  0x10000,   0x1C0000,
kernel.avm,  data, phy,     0x1D0000,    0x40000,
app1.avm, data, phy,     0x210000,   0x100000
app2.avm, [...]

The following is still supported:

# Name,   Type, SubType, Offset,  Size, Flags
# Note: if you change the phy_init or app partition offset, make sure to change the offset in Kconfig.projbuild
nvs,      data, nvs,       0x9000,     0x6000,
phy_init, data, phy,       0xf000,     0x1000,
factory,  app,  factory,  0x10000,   0x1C0000,
main.avm,  data, phy,     0x1D0000,    0x40000,
[...]

Question: do we want to keep support also for a lib.avm + main.avm scenario, or in general do we want to still support a lib.avm partition?
Right now it costs about 15 lines of code, so it doesn't add too much complexity.
I suppose that we might also support lib, kernel, app1 and app2 partitions with ho additional code for free, we just open lib.avm partition regardless of anything else.

[bettio]

Other additional schema that we might support: kernel.avm + main.avm (just a single app with kernel app that boots into it).