[Staking App] Button to stake is activated despite needing ERC20 Approval first

[dimsome]

Describe the bug
The button "Stake" is clickable despite needing ERC-20 Approval first.

To Reproduce
Steps to reproduce the behavior:

1. Go to https://staking.mstable.app/#/stake
2. Click on staking MTA or mBPT
3. Enter the amount in stake App
4. Lock appears, and is enabled, but "Stake" button is also clickable

Expected behavior
Throwing the error is expected if there is a missing approval. However, the Stake button should not be activated until such approval has gone through.
This results in users missing the approval button.

1. Simple solution: deactivate the button until the approval is done. Replace text with "Allow the Staking contract to use your MTA" or "Allow the Staking contract to use your mBPT"
2. Probably better solution: Add button above staking to create tx for approval.

See Uniswap example:

Screenshots

Trying to send transactions without approval throws an error.

[dimsome]

Non-consistent behaviour throughout the app, in another place e.g. Swap it's handled like this.
We should consolidate the behaviour and make it consistent

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