Allow partition table offset to be specified in `espflash.toml`, Cargo.toml `[package.metadata.espflash.flash]` or in the partition table itself

[jnross]

For different devices, different partition table offsets may be used. To allow this to be more explicitly configured, I propose that we allow the partition table to be specified in the espflash.toml file, or even in the partition table itself.
Proposed espflash.toml:

[flash]
mode = "qio"
size = "8MB"
frequency = "80MHz"
partition_table_offset = 0x8000

Proposed partition_table.csv:

# ESP-IDF Partition Table
#----------------------------------------------------------------
# Name,         Type, SubType, Offset,   Size,     Flags
# bootloader                   0x0,      0xA000
partition_table                0xA000,   0x1000
otadata,        data, ota,     0xB000,   0x2000,
emul_efuse,     data, 5,       0xD000,   0x2000,
phy_init,       data, phy,     0xF000,   0x4000,
cps,            data, nvs,     0x13000,  0x8000,
nvs,            data, nvs,     0x1B000,  0x25000,
ota_0,          app,  ota_0,   0x40000,  0x3e0000,
ota_1,          app,  ota_1,   0x420000, 0x3e0000,

Proposed Cargo.toml:

[package.metadata.espflash]
partition_table = "../../partitions-dev.csv"
partition_table_offset = 0x8000

[SergioGasquez]

Closed by #700