[docs] Fix typos and grammatical errors in SpanLimits docstring

[Dotify71]

In opentelemetry-sdk (opentelemetry.sdk.trace.SpanLimits), the main class docstring contains typos and grammatical errors:

1. "The limits that should be enforce on recorded data such as events..." -> should be "enforced".
2. "It only provides an a way read limits from env..." -> should be "a way to read".

Location in codebase: opentelemetry-sdk/src/opentelemetry/sdk/trace/__init__.py (lines 591-593)

Suggested fix:

class SpanLimits:
    """The limits that should be enforced on recorded data such as events, links, attributes etc.

    This class does not enforce any limits itself. It only provides a way to read limits from env,
    default values and from user provided arguments.

[Dotify71]

I will raise a pr in this issue within a short period of time :))